Oops. She shouldn’t have done it again.

A week after tickets went on sale for Britney Spears’ “Domination” concert series at the Park MGM in Las Vegas — fresh on the heels of a yearslong Vegas stint that ended last December — her first month of shows remains more than half unsold, sources told The Post.

By comparison, a 27-show stint for Lady Gaga that begins Dec. 28 at the same venue nearly sold out in the first week tickets were available. An Aerosmith residency that starts April 6 was 85 percent sold out in a week, according to sources.

It was only last New Year’s Eve that the “Toxic” singer wrapped up her initial Las Vegas residency — a four-year, 248-show run at Planet Hollywood entitled “Piece of Me” — which with a $138 million gross has her in fourth place on Las Vegas’ residency register.

Celine Dion leads the list with $385 million for her 717-show “A New Day” series (2003-2007), followed by the same artist’s $233 million take for her 399 “Celine” dates (2011-2019), according to Billboard.

Elton John’s extended “Red Piano” stay (2004-2009) ranks third, with $169 million.

Spears is launching the “Domination” series on Feb. 13 despite the fact that “Piece of Me” stopped selling out after its first two years in Las Vegas, an insider said.

The series was announced on Oct. 18 — less than a month after it was reported that 36-year-old Spears will have to pay thousands of dollars more a month in child support to ex Kevin Federline.

Meanwhile, Gaga and Aerosmith stand to benefit by being residency newbies.

Gaga’s critically acclaimed starring role in “A Star is Born” has her popularity at an all-time high, a source said. And Aerosmith and its boomer following have reached an age where both want to see each other while they still can.

The venue for all three residencies is the Park Theater — a 5,200-seat venue at the Park MGM.

Gaga announced her 27-show run on Aug. 13, Aerosmith went public with its 18 dates on Aug. 24, and Spears revealed her new 32-concert series on Oct. 26.