The AA-5B is a lovely airplane, but has no seat adjustment; so, Tortoise's suggestion of a lumbar seat cushion is the way to go.
You
must be able to push the rudder pedals to the stop, or you may someday find yourself unable to get out of a spin if you are unable to push the rudder to the stop
Spins are prohibited in AA products by the way which means that you become test pilot after half a turn or is it one? Those more knowledgeable of the certification standards can be more precise.