D Dovii kid I poured the same dimensions as you with .5 inch depth in some spots. You will need more than you think, I would buy a few more bags then if you dont need them return them. I used a mixing paddle in a 5 gal bucket one bag at a time, used around 4-5 bags. For an area that large you may have to push it around to level it out unless you make it extra watery.
Thanks dude. That was the plan. Did you use 50 lb bags? I know some of this stuff comes in 40lb bags