I'm going to ask my friends if I can go on a trip with them.
Why would you want to go with them on a trip?
I think they are talking behind my back, so I want to make sure they don't.
I'm sorry you are feeling that way. It's frowned upon to ask to be included in an event to which you haven't been invited. They won't like you very much if you keep pushing yourself where you aren't wanted.
They don't really act like my friends and they don't have a say in what I choose to do because I can go with them anyway.
I know that you feel worried that your friends are whispering about you when you are not around, but trying to keep tabs on them by nudging into their travel plans is interference and inconsiderate. Deal internally with your anxiety and paranoia rather than trying to control the people around you.