What nightclub? I also bounce in Boston, and have been for a few years now.
I'll echo what a lot of people have already said. The most important thing isn't necessarily size, it's your self-confidence and ability to speak and resolve conflicts. Ideally, you should never find yourself one-on-one with anyone, so you will never really need to square up with a customer.
As for size, I've worked with some real monsters, and I've seen some drunk 150 pounders go up and start shit with them, so size isn't really as much of an intimidating factor as you'd think. Also, keep in mind that you are definitely going to have to check your ego as a bouncer. I can't even begin to list the type of shit people have said to me, and all the while I had to smile with my hands in my pockets, but you're in the service industry, and that's what you're getting paid to do.