Standard salts CaSO4 2.5g, CaCl 3.0g plus a quarter tab campden. Tea at flame out in mesh bag, steep 10 min, leave bag in while chilling.
Based on boiling 7.00 gallonsliters at 1.046 for 30 minutes, this will decrease your wort by 0.50 gallonsliters, bringing your after boil OG to 1.049. You wanted an OG of 1.057. It looks like it will be under.