5 years ago, I'd definitely have called myself an introvert- except I used it as a crutch to justify certain behaviors that were actually harming my broader self development. Just do what feels right for you- don't want to go to that party? Don't! But maybe interpret it more as "I'm not feeling it tonight" rather as a consequence of an eternal truth about yourself.
Avoid thought patterns of the form "well of course I can't do X/of course this would make me feel Y- I'm an introvert!". Sure, I'm still more on the quiet "stay at home alone" side of things than most people my age, but I still did a lot of work on getting out of my comfort zone and getting better at small talk, and other silly social interactions, etc, and while it was painful at first it made me a much more balanced, well rounded person. It led to meaningful connections and friendships I'd never have had otherwise.
EDIT: can't agree enough with laynnn's comment.