"Also the bow is 71#s at 28,, I shouldn't need a special string should I?"
You'll need more strands than if you were shooting 50#, for a comparable amount of stretch/creep.
How much stretch/creep you get depends on a lot of things--how the string was made, the material, the number of strands used, temperature, etc. etc. etc.
My guess is, in your case, any number of the following could be the cause: string wasn't pre-stretched, it's made from dacron, it has 14 or less strands (dacron), it has 10 or less strands (most HMPE materials). You said it's new, and new strings generally require some shooting in, but not that much.
Chad