Am I a bad person?

I've always been a straight A student. I'm at university now. A lot of people still make fun of me for studying so hard. I have 3 friends. We help each other by sharing notes, explaining materials, copying homework, checking essays, etc. The thing is, those that aren't my friends are now asking me for the notes and help with essays since it's exam period. I am currently ignoring all of their messages that I've gotten. There are a few reasons for that:

1. I am feeling used since they are only interested in being friends when they need something.

2. I am already bussy with my studies

3. The reason why they don't have notes is because they've been going early from clases or not coming at them at all. It's not my problem that they aren't in class, but it's also not my problem that they are missing notes.

4. I'm tired of being used for these kind of stuff.

Yet I feel like a bad person for not helping. Am I?