I think it makes you a pervert. Any sort of sexual behavior which is not normal is "preverted". What you did is highly voyeurstic and bordering on a paraphilia although it's not that extreme. It is certainly creepy. If you were taking pics of a girl you hook up with and then jerking off to it later that would be a different story. The problem is the clandestine and maladjusted way you are going about getting off.

That being said, I don't think it's a huge deal because this isn't something you regularly do. In other words, it doesn't make you a creepy guy, it just means you have done some creepy things on a few occassions. Focus on the fact that you know better, won't do it again, and that the lapse in judgement was due to some paraphillic urges rather than an element of your personality. There's nothing so perverted about your sexuality that you should be ashamed of it. Sometimes you have urges and fantasies(?) about voyeuristically engaging women and on a handfull of occassions you acted on them in a VERY non-threatening manner. Some guys steal panties from their hook-ups. Big deal.