To set the default zoom, you can either set it in the program and then go to edit > 'save current settings as default' or select your value and run

gsettings set org.gnome.Evince.Default zoom 1.75

However, i think what you are really referring to is when, say you have a big zoom level of 175% and you have the sidebar enabled and continuous mode enabled, scrolling to the next page upsets the zoom. This makes the page go off centre and you have to adjust it manually each time, as the first screenshot below shows.

To change this behaviour, the only real fix is to select the 'fit page width' option by going to view > 'fit page width'. Then go to edit > 'save current settings as default'. This will eliminate the issue, as the second screenshot shows, although the zoom level will drop a bit as you can't set a zoom level and have the 'fit page width' option enabled.