Salts CaSO4 3.2g, CaCl 2,0g, MgSO4 pinch, plus half a tab of campden.
Based on boiling 7.00 gallonsliters at 1.044 for 30 minutes, this will decrease your wort by 0.50 gallonsliters, bringing your after boil OG to 1.047. You wanted an OG of 1.051. It looks like it will be under.