I bought plenty of extra for extra projects, but as long as you cut it right, you'll be ok. If you heat it, bend it, then cool it down and it doesn't look right, just heat it up again, re-bend it, and re-cool it. It's fairly "idiotproof" (I can vouche for that!).
Here are a few pics of my recently finished right shoulder bell (I posted the paints I used under the merged "paint codes" thread under "ARMOR"). This piece of Sintra took me about 2 minutes to cut with a Dremel (or less), a couple of minutes to sand, about 5 minutes to shape with a Wagner heat gun, then another 5 or 10 minutes scarring and denting it up with a Dremel to get the "battle damage". The rest of my time was spent painting it, and all told, I probably have about 9 coats of paint on it. All of the round "impact points" were made by heating the Sintra, then pushing into it with a dowel slightly smaller in diameter than the depression that I wanted to create. They range between 1/8" and 1/4" deep.
I swear it looks a lot better in person than it does here.
Sintra is your FRIEND!