It's perfectly acceptable to glance down at your horse's shoulder to check your leads in a pleasure class. That's a class that isn't judged on the rider--just the horse's performance. However, being able to feel your leads does give you that extra bit of polish that scores you bonus points in the show pen. When you're practicing, try rolling your seatbones deep into your saddle then ask for the lope. Concentrate on the motion of your pelvis. If you're on the left lead, your pelvis should rock forward and toward the left, and your left leg should feel like it's swinging forward.
Also, you may want to review how you set your horse up for a lope departure. Setting her up to get the correct lead will help you in the long run. Are you getting her body in the right position? I put my left leg on and ask for my horse to move his hips ever so slightly toward the inside of the pen, then give a soft cluck to cue the forward motion. By setting up his body this way, I'm making it easier for him to reach forward with his inside (lead leg) and with his outside leg. This might sound fuzzy when you read it, but try it a few times and it will start to make sense.
editted to add: I just read where you said he will drop his shoulder on you. The second he does that , pick up his front end and spin him in the direction of the lead you were asking for. And I mean SPIN--hard and fast. He knows better, so make his find out that doing the wrong thing means more work for him. Let him settle, then ask for the lead again. If he gets it right, let him lope on for awhile with no correction.