That happened to me once while testing, and it was resolved by just refreshing and trying again. I'm not sure if that will help.
Right now, our best guess is that our game file is kind of big, and connection/ download may have something to do with loading it. I just had a friend who wasn't able to play either, so that's our best guess as of now. Really sorry it's not working! we hope to fix any bugs that pop up (including this one) once the rating period has ended and we can edit our submission.