don't be paranoid. if you had gyno, you'd know it. A full nipple doesn't = gyno. You'd have swollen plump little titlets.
As far as filling up the chest, barbell bench is better for increasing power. Using dumbbells is better for size and development of the pec than a barbell press. You get a better and fuller contraction of the pec using DB's.
If you care about strength, I'd go with the barbell press. You will uundoubdetly get chest size gains. If it is purely cosmetic, then DB press is better.
Rep range in the 8-12 rep range. 12 reps would mean failure. Increase your amount of sets. If you have to drop weight to make it to 8 reps after 3-4 sets, that's fine.
when you focus on the lift, make sure you are focusing on the chest making the contraction as opposed to pushin the weight up with your arms. That's why I prefer dumbells because you can concentrate the chest better each rep. The BB press is limited in its range of motion.
And, some people are gonne cry foul, but flies will have an added effect to the chest. Do them AFTER ALL your pressing is done.