You can 'edit' delete your text inside the OP or any other post in the thread if you want, but you can't delete a thread itself once it gets 3 replies. Then only admins can delete the thread.
But, really, sweetie, don't fret about it. Most of us say stupid shit in forums at one time or another. Some do it so regularly I've come to the conclusion they can't help themselves.
The good news (I guess it is good news) is most people don't give much of a shit what anyone says and will have forgotten it within seconds of having read it. Think about it for yourself... how much of the stuff you've read on this or any other forum do you truly remember or even care to? Or, put another way, what you say is generally WAY more important to you than anyone else.
What REALLY matters is your tone over the long-haul. Think of it as 'forum cred' if you like. If you keep posting and begin saying something *interesting* that isn't totally narcissistic, people will get to know and like you.
Also, you are *very* young. Youth (and 'the hot') is often forgiven its indiscretions far more readily than those who are presumed to be more 'mature'. (Which I always equate with 'full of shit' because 'mature' rhymes with 'manure', but that's just the way my weird brain works.)
Or, put another way, just chill, dude. No sweat. It's all good.