Fermenter volume low due to lid off boil. Next time add 1/2 gal at flame out. Double ground, straight recipe, excellent result.
Based on boiling 6.70 gallonsliters at 1.075 for 60 minutes, this will decrease your wort by 1.00 gallonsliters, bringing your after boil OG to 1.086. You wanted an OG of 1.088. It looks like it will be under.