Ok, I am going to show my lack of knowledge/experience. I have a 62" longbow and I am trying to finish "grinding" the limbs down. It was started by my mentor and is measuring 62# at 25". Yeah it is a stout little bow! Anyway here is the problem. When I string it up, it shows to be a good 3/8" off center. What can I do to bring it back to center. The limb tips and nocks are finished so I don't have much to work with there.

So it's 3/8 off the center line? Sounds like you might need a new mentor, if he was the one who finished out those tips without checking center alignment. Maybe if you introduced some propeller twist into the limbs, you could get the string in line You might think about making those tips real tiny and reinforcing them with overlays. 

"I am trying to finish "grinding" the limbs down"

That could be a problem, explain what part did you grind on?

I was trying to take some poundage out by working down the limbs from the fadeouts to about 6" form the nocks. I don't have any twist. It has just pulled off center.

Don't think you can correct that. By the time you have it ground back the limb will be pretty narrow. Put a string box to nock to nock and put it in a vise. Leave the string in the straightest limb tip and swing the other to get the string centered down the limbs. That will show where the material has to be removed. Lots of ways to check limb alignment but on that short a bow it will be tough.

If it's a one pc maybe make it a 2 pc and straighten it in the process?

Not familiar with a string box.

which way is it off? Away or towards the shelf?

It is off away from shelf.

Maybe you could pike it by 1" each end realign the center and side tiller some weight off, at your short draw you could probably narrow that bow up easely ! Welcome to bow making problem solving 101