Salts CaSO4 1.0g, CaCl 0.6g, plus a quarter tab of campden. Chill to 10C before pitching, ferment at 11C.
Based on boiling 7.00 gallonsliters at 1.045 for 30 minutes, this will decrease your wort by 0.50 gallonsliters, bringing your after boil OG to 1.048. You wanted an OG of 1.050. It looks like it will be under.