If you don't want to do something, don't make excuses. You are setting yourself up for problems, being taken advantage of, and making enemies out of your friends.

I know socializing is getting harder and harder, so use this as a newbie-zone, level-1 exercise in having a little self-worth. Just say "No I don't want to go, it's not something I'm interested in."

And learn to just let that sit out there. If you have people who are going to interrogate you and try to push you into doing something you clearly said you don't want to do, they're not being friends, they're trying to use you for something.

Now all that said, don't be anti-social. If there's no reason not to go, if you just aren't feeling it, get off your ass and go. Stop making up excuses for why you're avoiding other people, you are getting stuck in a cycle of avoiding human interaction, becoming depressed as a result, which makes you want to avoid human interaction. Sometimes you have to force it back on track. Put effort in and life will pay off more. Stop sitting and ruminating, your brain will become your own worst enemy.