Is that normal practice in any style of aikido, to have rank newbies participate in exam-prep classes? I feel very apprehensive of returning to the dojo, also very apprehensive of getting scolded again for something that I'm really not sure should be my fault.
First off - I do. I don't have beginners classes and every one does everything that everyone else does. The partner is very much aware that the person is a new and demands are adjusted accordingly. The beginner also has a certain responsibility to self to judge what they can and can not do safely.
Scolded for something you didn't do. Well mistakes happen - both yours and others - what's the big deal. Learn from it if you can.
Sorry about the injuries - they happen but, especially with beginners they shouldn't.
The hair being stepped on. How long was your hair? Did you just lay there and wait to get stepped on? Generally, crowded conditions or not, you should be up on your feet pretty quick.
Neck injuries from roles bother me a little more but really - could you have stopped and taken a slower role?
I'm not coming down on you but after four lessons, most of which you enjoyed, I don't really see a reason for angst.
Again adjustments are made for beginners but the class can't revolve around them. Otherwise those that have put in the time and effort will not stay.