Find a gym that has competing amateurs. Go at least 3 times a week. Spar as much as you can with as many different partners as you can. Try to run a few days a week to start, if your really serious run every day. Your coach should start taking you seriously once he sees your there lots and putting in the work. Adult boxing class to me sounds like "boxing fitness" and not training to fight in the ring. If this is true its probably about as useful as going for a run but nowhere near as effective as the training most amateurs do daily. Tell your coach you want to fight after you've shown your coach you want to fight. The minimum work the amateurs I train with put in is 3 hours a day, 3 days a week at the gym and 10+ miles a week running. The serious fighters do alot more than that. If you've been training 4 months already it shouldnt take you long to get ready for your 1st fight. At our gym most comitted fighters have there 1st fight within 3 months to a year of starting.
You'll learn alot more sparring people better than you. Focus on defence such as stepping back and to the side to get away from their attacks, shelling up when you can't get away and keeping your gloves up. Im not sure what level your at but those basic strategies should work. Also you gotta really look at what advantages you have, are you the taller guy? Do you outweigh your partner? Does he tire easily? Fight your fight not his. I'm usually the taller guy so when I'm against someone more skilled than me I sometimes just stay out of range and jab them the whole round. When im the heavier i sometimes throw my weight at them.