Life results in injury. in the past two months I have hurt myself a few time... note I hurt MYSELF. No one actually hurt me. Well unless you count Sunday's Nikkyo but then I did resist a little and it didn't do me damage.
Injuries can happen and maybe they will happen but I don't think its really a big enough concern to keep you from practicing aikido. Just use your head and do things as you are taught. And don't resist. Any physical activity has the potential for injury.
Go try a class or two and don't stress about it. Your going to wind up scaring yourself out of trying something you may just really enjoy.