You shouldn't feel like a loser! Isn't that what being an INFP means? Not being social? We are introverts after all.

You should accept yourself for who you are, not who society thinks you should be. If you don't like parties don't go to them. There's more to life than "being cool" and stuff. If you really want to be more social just keep trying, but don't beat yourself up about it if you can't.
By the way, I think people who don't go to parties are much cooler than those that do. What's at a party anyway? Drugs, alcohol, stupid people? Granted, not all parties have those things. But still, they seem boring to me.
Hope this helped

Just so you know, I'm in high school, so i can relate. XD That sounded lame!!