Oh, you are going to love quilting!!!!!! Don't be discouraged, I haven't been quilting long either and I found using the rotary cutter took some practice. Really, take your time cutting, it's worth it to be accurate. Use a plastic ruler, and put your rotary cutter right up against the edge (after lining it up), cut away from you (moving your other hand as necessary to keep the ruler in place). But, don't be worried about messing up fabric. Like the old saying goes, Practice makes perfect!
(One other bit of advice (boy, you're getting a lot, huh?), don't pick a design or block too hard to start out. There are lots of designs that look fantastic all made up that are very "easy".)