Am I in the wrong?

My birthday is on Monday, so my boyfriend and I were going to go out Saturday to go to dinner, a bar, and run a few errands (get my car fixed). His best friend and his girlfriend have a day off on Saturday and want us to go to the mall in their city (an hour away.) l told my boyfriend I want to do what I want to do on my birthday, but he’s acting like I’m being difficult. He says I don’t want to hang out with them because we’ve only met them once in the 2 months we’ve been dating, but our days off simply never line up. Am I wrong for wanting to do what I want to do on MY birthday?