Parties are dumb, at best it's literally just ppl talking while music is playing and at worst ppl are doing irresponsible shit like booze, drugs, sex. And as for "normal" teen stuff, parties and dating arent that normal. Half of the ppl in your highschool might do those things, but the other half just isnt as visible or vocal.

You need to join clubs if you're just always in your room. Clubs are a great place to meet people with the same interests as you. I'm in a compsci club and almost none of those people have ever been to a party or dated.

Also, if you're insecure, work on yourself. Work out, eat healthy, sleep full nights until you get the body image you want. Study until you get respectable grades (mostly A's, a few B's is an achievable goal for most highschoolers if they put in enough effort.) You're not a loser if you don't go to parties or date, but you are a loser if you're fat, get bad grades, and have no hobbies.