Too Nice?

I don't know if being too nice is such a bad thing, but in some circumstances, I feel like it is. Around people I like or respect, I am always nice to them and considerate. But I feel that sometimes I give up too much for the sake of someone else, and they would not do the same for me. It makes me wonder whether I should continue living like this, or take karma into my own hands and treat people how they treat me. This is possibly a stupid example, but today I had my algebra midterm first thing in the morning, and then since I have 4th period lunch, I could leave early. I could have been out of my high school by 10 AM at the absolute latest, but I ended up being in school until 1 PM. It was one of those incidents where I took on too many things without realizing how I would regret these decisions later on. Originally, my plan was just to have my father or grandfather pick me up from school after my algebra midterm. However, my friend also had 4th period free and wanted me to stay with her. She wanted to study for bio with me, and even if we procrastinated studying, spending two hours with her is always pleasant. I agreed because I didn't want to make someone come and pick me up when I could always stick it out for two more hours and take the bus. While these thoughts ran through my mind, I wondered briefly if this was a legitmate reason or if I was trying to convince myself that it was. Then, one of the girls in my journalism class sent me her articles to edit, and mentioned that she was staying after in Mr. B's room both Wednesday and Thursday. Without thinking properly, I offered to stay after with her. After all, I am here editor. She said that was really nice of me, which was all the validation.
It wasn't until this morning that I realized I did not want to do either of these things. Really, I wanted to go home and take a nap and read a little, and then be rested so I'm not exhausted when I study for bio. I stuck through the two hours of doing NOTHING in the commons and then stayed after with the girl from my journalism class. Did I mention that I almost had a heart attack because I realized that she never emailed me back to confirm she was staying after? Yeah, I practically ran into Mr. B's room and asked breathlessly, "Is Allison staying after?!"
She was, to my relief. But it was also on the verge of torturous because, unsurprisingly, she has no layout done. Does she honestly expect to fill and properly lay out three pages in a few hours? It's not such a stretch for me, but I've been laying out in Adobe In Design for a year. I know how to work the program. She doesn't. I'm willing to help her, but really, should I be taking an hour and a half of my free time because she waited until the last minute to work on this? It is not even my project, and I was more anxious than she was.
I wonder if some of my actions are within reason, or if I convince myself they are.

On a spontaneous note, I am officially in Outsiders withdrawal. My uncle, who teaches alternative, drop out, and special education students in Shelton or Stratford or something with an "s," had his classes read the book. I don't know if it's part of the curriculum or if he thinks they can relate because half of them are probably in gangs. They finished the book, and apparently the class enjoyed it, which is good. Two or three weeks ago, my uncle borrowed the DVD from me, and now I miss it. Maybe knowing that it's not in my house, knowing that I cannot watch it if I want to, is what's making me miss it so much. Either way, I wanted to watch it as sort of a celebration of me making it out of my midterms alive and unscathed. Oh, well. I have Kinnari's sweet 16 party this Friday night anyway. Part of me is looking forward to it because I get to see my close friends, but part of me is absolutely terrified because
A) dresses make me feel awkward,
B) put me in anything but flat shoes and I will break something; "something" applying to both body parts and breakable objects
and
C) I don't dance.
I don't even have the ability to dance. That cotton eye joe shit everyone knew in elementary school was way over my head.
Also, I simply don't have the ability to loosen up and unravel like that in front of people.
That sort of makes it sound like I'm one of those people who blasts dance music while home alone and dances in her socks and a boa, with a brush as a makeshift microphone.
I am not one of those people.
I just don't dance.
Worst of all is that all of my friends are going to push me to do it, and they don't realize I can't.
Kinnari told me, "I'll get Liz and Jill and we'll teach you how to be a hoe on the dance floor!"
How am I supposed to say no without sounding like a bitch or letting them down?