I used 10 lbs golden promise, 2 lbs of Munich and 4 lbs of 2 row
Based on boiling 7.50 gallonsliters at 1.066 for 120 minutes, this will decrease your wort by 2.00 gallonsliters, bringing your after boil OG to 1.084. You wanted an OG of 1.088. It looks like it will be under.