I looked at the product page and it says 1 scoop = 300 mg magnesium
So you took 7*300 = 2100 mg magnesium per dose.
I have searched and found out that the amount of elemental magnesium in 1 tbs of Epsom Salts is 10% the weight of salts. So, in 1 tbs (15 grams) of Epsom Salt we get 1.5 grams i.e. 1500 mg of elemental magnesium.
I have a similar product and I think 5 scoops would be enough for me.