Is it wrong that I beat on my sister's bedroom door while she was in there with her boyfriend?
Why would you beat on your sister's bedroom door when she was occupied?
They were being so loud and I hope to ruin their mood and concentration
I understand that you feel your sister and her boyfriend were making too much noise, but it isn't nice to be cruel to her. Simply ask them to be quiet.
I thought that if I say something to them, they might think I'm being annoying and be more upset.
Although they were being loud, beating on the door is disrespectful to your sister. It would be best to just talk to her about the situation when her boyfriend is not there.