Using gitlab.pavlovia.org you have an advanced interface for your projects that allows various customizations and I think that allows you to change the name. BUT there are various problems with that because the name defines the URL that the project lives at too. So, for instance, when you’ve changed the name your local copy of the repository will probably now point to the wrong location. That can be fixed with some git skills, but I don’t know what other knock-on effects there will be.
Basically, I think it would be safer to create a new project with the corrected name.