Do you have it high on the neck, below the ears?
How are you walking with your dog?
If your dog is heeling on your left, and you have a 6' leash, put the handle in your right hand and hold the slack of the leash with your left, loosely so you can "pop" if you need to and to also keep the leash from getting tangled underfoot. The palms of your hand should face down, and see if this gives you more control. The "pop" should be a quick jerk to the side and not a constant tenseness or pull on the leash.
Are you giving the verbal command to heel when in this position?
Ideally you should find a good trainer to help you in person. A trainer can evaluate what else is going on with your dog, plus remember it is still a pup it's not going to be a calm mellow walk with a pup. I'd practice heeling for 10 min 2x a day.