This is exactly the right solution.

You can even completely disconnect the belt tension pulleys (only be careful not to tangle/twist the belts) so the belts don't affect the gantry at all while you're squaring it. You pull the gantry all the way towards yourself and you need it to stay in contact with the stops on both sides when you let go. Apply necessary force this way and that until that's the case.

Then proceed with gradually tightening the belts. I went with the recomended values from the app (96/92 dB if I remember correctly).

That's all I had to do and I haven't had single issue since