Fun game :) I really like endless runners, so I've enjoyed the idea.
It's a great submission for the first gamejam and also it might be easily upgraded to look and feel really well :)
Some suggestions:
< In LightingSettings you can change skybox to none and on MainCamera set SolidColor and make it black, it would make game look much more better with black background :)
< I like the idea of using rewind as save point. Hope there would be a bit of difference on taking a blue square, for example changing mechanic to flying instead of walking, but it's nice that it changes shape anyway ;)
< Some music and sounds are always good to make your game feel better, even if they are just taken from some free site.
< If you work with primary shapes it's good to put some emissive material on them, it would look really cool.
Anyway, a great game! Hope you upgrade it in a future.