congrats on your bike!
I read your other post re: the bianchi and the specialized... great taste in bikes! (i'm drooling over the specialized rockhopper... bought a 3-yr old bianchi as my first "real bike" last fall )
the rear brake is probably just out of alignment... if you can wiggle the arms back and forth, you could prob. tighten it yourself with an allen wrench (hex key) so it stays straight... at least, that worked on my cruiser (i don't know a whole lot about brakes, or how much they've changed...) i'll bet the lbs could fix it while you wait, though, or show you how so you can do it in the future never fear, saturday should be lovely riding weather in Michigan (at least, i hope! my mom is visiting and we're planning a long ride!)
if you want to learn to turn a wrench, try out Bicycling Magazine's guide to bike maintenence... it has good directions and pictures, and it's the only way i can save face around the guys (i can now lube my chain, fix a flat, adjust my brakes, and remove/replace the wheels... but not much else yet...still have some reading to do! ) sometimes your LBS will offer classes too... i'm planning on taking one this summer.
last time i brought my cruiser in for a tune-up the lbs washed it off... but it was reeeeaaaaally grimy (i had taken it off-road for a mtn race... not reccommended ) so i think they had to wipe it off just to see what was going on!
have fun with your new bike!!! happy riding!