I'm going to add, please don't expect aikido to provide conditioning training. I've trained in aikido for 4.5 years and for 3 of those years I was clinically obese, not very physically strong, and had no stamina. Aikido kept my weight and health from getting worse, but it by no means got me in shape. For the past year and a half I have gotten into shape by doing aerobic weight training. I've lost 35 pounds and improved my physical strength and stamina. If anonymous is weak (I'm getting the impression that anon is either very petite, old, disabled or really out of shape) then some form for weight bearing exercise like light weight aerobic weight training might be better, especially if your goal is to improve your strength. Just to let you know, being able to train at the level I wanted in aikido was my motivation to work out and lose weight. So, I'm not saying give up on aikido, but use aikido as your personal motivation.
I agree with everyone else, you train at your partner's skill level. And I don't know why you were allowed in a testing prepatory class. We have those for people testing for 1st kyu up, and believe me they are intense. Only 2nd kyu and up are allowed to attend.
I train in an Aikikai dojo and we're known for being "hard" compared to alot of other Aikikai schools, but we still go at the pace and skill level of the uke. One of our 2nd kyus is a 61-year-old transplantee and no one pushes him past his abilities. So please don't discount the other school just because you heard someone say that they are "hard" or "rough". Go there, watch a class, do a class and see how they treat you.
I think what Peter is getting at is that we still have the responsibility to protect our own saftey. Please...please don't forgo your intuition when you walk into a dojo. It's okay to speak up and say something. But yes, you were in an advanced class and maybe some should have asked if you were okay with it.