I was browsing on Facebook a few weeks ago, and I found that one of my pages posted a photo with cringable grammar errors. But then the majority of the people commenting commented on the incorrect grammar...incorrectly. Past tense and past participle are different things, and people seem to not know the uses for them, which saddens me :[
But yes, the correct way to say this sentence would be "If you haven't hidden."
EDIT: Sorry the photo is so small. It was bigger before, but it was the size of the moon and it looked awkward :(