Yea, the size was the problem. When the image is that small with intricate cuts like letters, the plotter tends to cut innacurately, and that's why you'll notice the letters came out somewhat crooked and uneven.
If you're gonna do this more often as UB/US grows, you might consider buying a vinyl plotter. The smaller ones can handle 4-8" wide stock, and you can get them for about 200-400 bucks. Hooks right up to a PC or Mac, and includes software. Could save a ton of dough in the long run.