I'll just put on a nice woollen thermal top instead. That should keep me warm enough.
Your instructor's obviously not working you hard enough! Seriously though, I'm 6'2" and I have no problems in the 152. I suggest your sore shoulder might be the result of an involuntary effort to keep out of your imstructor's 'space', which, after an hour, could be hard work. Added to which are the tensions of your first few lessons (I was always being ticked off for being too tensed up -
"RELAX!!" 
) so there could be your answer.