This is really infuriating.
Try and submit a new puzzle. Take your time, make it a good one. Research it, test it, not only for your puzzle author's solution's correctness, but also for any pitfall that a beginner could encounter while solving it. Verify the edge cases, test against the constraints, adjust them to make them a more natural fit.
Then submit it. Oh, but make it realistic. Your cat might have distracted you, or maybe there was a subtle earthquake at the same time, anything. Just misclick the submit button by a few pixels, no need to aim for anything fancy. Or press escape, that works too.
It's all gone. No confirmation. No way to bring it back, be it by attempting the browser's back button, or hoping for some angular-style caching that would make it pop back when clicking the Contribute button again.
Who in their right mind thought that was reasonable UI design?!
MISCLICKING IS NOT AN ACCEPTABLE SUBSTITUTE FOR AN ACTUAL CANCEL ACTION.