Hop bags used for 6 ounces of hops, not first 3 ounces.
Based on boiling 8.00 gallonsliters at 1.075 for 60 minutes, this will decrease your wort by 1.25 gallonsliters, bringing your after boil OG to 1.087. You wanted an OG of 1.081. It looks like it will be over.