This is your first time sparring after lots of bag work? Accept one simple fact. You will be very frustrated at your inability to land good punches and that is with him merely moving, not using his defensive abilities or hitting back. This always happens, at least in the dozen years I've trained fighters- didn't pay attention before that. On the bag you can plant your feet and let 'em fly. with a live target you'll find him too far then to close, you'll ee an opportunity and it will seem forever for your punch to get on its way. You'll learn to shorten up your stance and to punch without telegraphing blows by drawing back- all motion goes forward. Use your jab, move around and get acclimated, concentrate on defense... but always with an eye to setting up a particular punch. Remember that sparring in the gym isn't fighting. It is learning and improving your skills.