Keep this in mind: when in your stance, try to swingyour arms back. If your elbows miss your ribs they are too far apart. This not only exposes your body to attack but takes power from your punches, which you most likely telegraph any way. Watch in the mirror- see how high elbows tip things off. Also, on the heavy bag, practice stepping around it- small steps and quickpivotswill get you out of range w/o having to move a ton.
I'm betting you'll do ok. Keepin mind that landing goodpunches is harder than it seems; most everybody is disillusioned the first few times because they just cannot land a good one. But if you keep calm you'll see learn and remember for future rounds, and have a ball, which is the point. (if the opportunity is there see if you can spar a round using just jabs- after you do what you are prepping for- as that is fun. You have to think and work to land in that situation but its great for getting used to jabbing and avoiding a jab simultaneously)