I don't feel lonely or social
Do you feel like this all the time?
Depends on when you ask me.
Not everybody feels like socializing all time; some people do at certain times and other people don't. As long as you don't break plans that you have made, then people will understand when you don't want to hang out.
I just feel better when I'm alone.
I do agree with you that nobody should be forcing you to socialize if you don't want to. If something like this happens, though, just tell them directly that you are not interested. It is not okay to react with anger in those situations, as the other person was probably just being enthusiastic.