Is there no way this movie would be made today?
Not necessarily because of any political correctness issue. I think that Can't Hardly Wait is so popular today because it reminds us of more cheerful and "simpler times" back in the '90s (i.e. post-Cold War, pre-9/11). It's one of those movies that comes every few years that perfectly encapsulates how high school/teenage life was (in this movie's case, roughly 1997-2001). Can't Hardly Wait is really just a '90s version of a John Hughes teen movie.
But with that being said, I think because we may have likely become more cynical and pessimistic, that it's easier to pick part what may be most troublesome about the plot, namely:
*Preston is pathetic, creepy stalker and not just a dogged nice guy after the girl of his dreams
*Preston and Amanda in reality (and not a fairy tale) wouldn't stay together for long
*How gullible must Amanda be to be immediately won over by this strange, secret admirer's "love letter"? What exactly did Preston write that was so enchanting that it won her heart? Something like that would probably be written off as corny.