I don't know how many fat 8ths are in a pack, but I thought a charm pack was 42 5" squares. Two of those would be 2*42*5*5 = 2100 square inches, while the quilt you want to make is 60x72=4320 square inches. You will wind up with more of your supplemental stash fabric in the quilt than charm fabric, not that it's a problem, but you should be aware of that because it might influence the type of pattern and/or the choice of stash fabric.
So, how many fat 8ths are in a pack? I looked on several sites and the amount seemed to vary.