I'm happy I set my brother up
Why would you be happy about something like that?
It's just that he is very annoying and always hits on me.
It is a little odd that you feel he hits on you, but you should still try to have his back. Siblings should always try to look out for one another.
It's my choice. I just hope mom doesn't find out that I set him up.
I know siblings can be annoying and it's possible that you're wrong thinking he hits on you. It's better if you talk to your parents about his behavior rather than setting him up in something. After all he's your brother and you're expected to help him if he's doing something wrong.