I agree with very much of what Sadathrion writes in his answer, so I'd just like to add to it ... and, uh, it didn't fit in the comment box.

Mind, that I am from a standup art and don't know a whole lot about grappling, but the same principles should apply.

##Take it up with your instructor Suggest you change partners from time to time. In our school, we often change partners several times during class. Everybody is different, so the idea is to try the techniques on different people. What works on someone, might be useless on someone else – or need some tweaks in order to be effective. Some times the instructor will purposely mismatch us.

When we do sparring, we change every two or three minutes. Everybody lines up in two rows, and then rotates to face a different partner every time. At the end of the class, you have usually partnered up with nearly everyone.

Ideally, you will always be paired with someone slightly better than you, as that is when you learn the most. (Beginners never appreaciate the luxury they have! :) ) In free sparring, the more experienced fighter can choose to focus on some of the things they are not so good at. Or purposely let the junior student have some leverage, and work on defense rather than offense. That way, it will be a learning experience for everyone.

In any case, it is the duty of the senior student to give the junior student a fair challenge (it sounds like some of your classmates are rather intense) and help them become better, as their own senior students helped them.

Now, you can't always just pair up with some random person. If for example we are dealing with a strength excercise involving lifting or carrying the other partner, then naturally it will make sense to find with someone of similar size. Likewise, if some of the senior students would like to practice intensly due to tournament preparations or the like, then you might not pair them up with beginners.

##Find out what your strengths are, and utilize them Not every student is the same, and we all have our strengths and weaknesses. The biggest person is not always the "strongest" fighter. A smaller fighter is usually faster, more explosive and more flexible. Generally speaking, they can learn to do more advanced techniques with greater speed, precision and still avoid being caught themselves.

Find out what you are good at, and then use that against them, so they will be more challenged.

##Don't be afraid to ask questions Your situation is unique, in the sense that you only have training partners that have much greater physical strength – and for now at least, probably also superiour technique. It is possible that many of the things that are shown to the class, needs to be tweaked in order to work in your situation. Ask your instructor and partner for help if you "get stuck".

##Recruit friends! You mention that your friends think it's weird to roll around on the floor with sweaty men – which is understandable, it doesn't sound like a very attractive sell. Perhaps you could persuade some of them to watch, maybe that will open their eyes. Or you can beat up the school bully, that will get you some attention. **

Have you tried asking a male friend? They might be more open to the idea. However, given your age, I understand it might be awkward to ask boys on after-school activities. :)

But definitely get your brother involved. If for nothing else, maybe he in turn can recruit some of his smaller friends. I mean, if he doesn't join now, in a year or two he will be beaten up by his little sister! Embarrassing!

##Get out some When you start to see some progress, have a chat with your instructor again. Hopefully there is a seminar or even tournament you can attend, where you will be able to test your skills against a more equal opponent.

This first challenge might go both ways. Perhaps it will be super awkward and difficult to roll with someone on your own size – their speed might be very different from what you are used to. Or you might completelly crush them, since you are used to heavier guys. :)

Either way, keep at it!

** Attenttion! Actually beating up the school bully is not advised. Society is not yet ready to handle random acts of violence, even from small girls.