Do you mean you roll off to one side or you just end up facing another direction other than forward?
I think that the first could be changed with a little bit of a tweak in the angle you enter the roll but I'm not entirely sure on this one.
I don't think the second one is a problem at all that's how I used to roll.
I say "used to" because I recently lost my rolls because of school and when I tried doing one on concrete off a short drop I hit mah butt bone and it's been hurting for a while xD Funny thing is that I had done other, good rolls, before that. And on the same drop too!
Okay back to you xD
I'm assuming you've been rolling on grass? Try finding a place that's mostly dirt or real short grass before moving on to concrete. It won't really hurt if you're doing something wrong but you'll be able to tell fairly easily if something is wrong.
The best advice I could give you is practice practice practice
I'm assuming you're also rolling on grass. If it's tall, cushion-y grass and you're feeling discomfort behind the shoulder most likely you're slamming yourself onto the ground. I remember I used to slam my shoulder into the ground because....I guess I would tuck for the roll too early before I even touched the ground. This is because I didn't use my arms at all. I would just tuck them under my body. Your arms are a big part of your roll in my opinion. Try absorbing some of the force with your arms. Not all of it of course but just enough so that you can get a smooth rolling motion from your hands to forearms to shoulder and all the way through
Maybe that could help.