My riser angle on one side is 21degrees on the other side it is 21.50.According to my mesurements.I am using a protractor that kids use in school. How is it important is th 1/2 degree.

I would think the total angle is what would be important as the riser will be in the middle. At about .008 per inch (.5 deg.) that won't add up to much.

I don't think you will see the .5 degree difference- you can do a quick check to verify using the "Hera" method. If the limbs are equal in weight and you can't see the difference- you should find that the 21 degree vs. the 21.5 degree will end up being the bottom or stiffer limb.