Unfortunately the problem with anonymous postings such as the ones on ThisCrush, there's no way to verify your identity so you'll be unable to delete a crush once you've posted it.

The best you can do is ask the account owner to delete it from their page, but then of course you're admitting you were the one who posted it.

Always be mindful of what you post and the consequences of your actions! Be nice, and you'll have no problems on ThisCrush!