ive done mma for 4 years and a martial art for much longer before, a mate of mine is a boxer and we did this at the last 3 parties we were at together and even while crossfaded as all hell he still managed to only tag me 3 times in 6 rounds. its the most fun thing to do though with you and a mate.
You're developing bad habits. Hands up. Chin tucked. When you throw a punch, throw it just like a power shot with your hips and everything in it (but pull back to avoid hurting your partner). Sparring is simulating a fight, so don't just play tag with your hands.