​The principal of an Anglican school says she “didn’t realise” a letter she signed would preserve the school’s right to expel gay students or sack gay teachers.

Dr Julie Townsend of St Catherine’s School in Sydney’s eastern suburbs has become the latest principal to distance herself from a letter, signed by 34 Anglican schools, that is rapidly losing support.

On Friday, the first of the signatory schools announced it would officially retract its support for the letter. The joint heads of Blue Mountains Grammar wrote the events of the past week had “damaged our school” and hurt members of the community.

The headmaster of Shore on Wednesday described the decision to sign the letter as “the most humiliating moment of my career”, and two other schools have also apologised for the unintended harm caused.

But when asked if they would rescind their signatures, Abbotsleigh, Barker College, St Catherine’s and Shore did not respond. On Saturday, hundreds of former students plan to march in protest from Abbotsleigh to Barker College.

Last week it was revealed that the 34 schools had written to the federal education minister demanding that he preserve a section in the Sex Discrimination Act that allows religious schools to discriminate on the basis of “sexuality, gender expression or marital status”.

The principals said they only wanted to preserve “the ethos” of their schools and would not actually use the exemption to discriminate against gay students. They described the exemption as “clumsy” but necessary.

But on Thursday, Townsend told parents she did not even know the wording of the exemption was amended in 2013 to include sexuality, therefore tying the letter “unwittingly” to sexual orientation. .

Apologising for any hurt she had caused, Townsend wrote: “I am sorry I was not aware of the 2013 change to legislation. In hindsight, it gives a very different slant to the letter we signed.”

On Friday, Blue Mountains Grammar went further and retracted support for the letter itself, saying their “ethos” was opposed to keeping the exemption.

“Quite rightly, many members of our past and current school community have found this hurtful and offensive,” wrote joint leaders Megan Hastie and Andrew Beitsch.

“Our ethos values equality and inclusion … for this reason the school withdraws its support for the retention of the provisions in the Sex Discrimination Act as stated in the final portion of the open letter.”

Townsend, and the other principals, have committed to fostering “inclusive” atmospheres for LGBTI students, but none have offered to rescind their support for the letter.

Scout Boxall, a former school captain of St Catherine’s, said it was hard to believe Townsend did not know what was in the exemption.

“She should know the 2013 exemptions are there,” Boxall said.

Boxall believed Townsend and the other principals had been pressured to sign by the Anglican diocese of Sydney.

“She has realised that signing this was a huge mistake and is trying to backtrack as best as she can … I just think it’s really embarrassing.”

Townsend declined the opportunity to comment.

On Tuesday, the head of Barker College, Phillip Heath, wrote to a student that the letter was signed in response to a request from the diocese.

In response to the statements from Anglican schools that they created inclusive atmospheres, former students from other signatory schools shared their experiences of homophobia and transphobia.

Maddy, a former student of Abbotsleigh, said teachers had failed to clamp down on homophobia, and visiting priests directly said homosexuality was to be hidden.

“In a class discussion in PDHPE [personal development, health and physical education] about sexual health, one of my friends asked about gay sexual health, and another student said gay people should go to re-education camps.

“The teacher didn’t really censor it, and I think it should have been reprimanded …The school would say you are allowed to be homosexual but you are not allowed to act on it without it being a sin.”

The headmistress of Abbotsleigh was contacted for comment but did not reply in time for publication.

Oliver Stiene, a former Blue Mountains Grammar student, said that when he came out as transgender, he was told to hide the news from other students.

“There were a lot of teachers who were supportive and did try and help as much as they could [but] they wanted me to not change my name on Facebook, or not tell any of my friends,” he said. “Everyone knew in our year group. Nobody cared. But the school kept saying they wanted to look after the wellbeing of other students.

“I see a lot of younger kids, it has really shocked them. I have a friend at the school at the moment. He’s gay and he is very nervous to go to school. And I feel so sorry for him.”

Beitsch said he would apologise to any student who raised issues of discrimination.

“The school has no record of any complaint of discrimination based on sexual preference, but if former or current students believe there is an issue I would invite them to come and speak with me directly and, if an apology is due, then it will be given and, if change is needed, then it will occur.”