I would make the borders of the pond more irregular instead of straight lines. I think the bottom of your pond will look ok the way you have it painted. How deep is your pour. Just completed a lake and river with two part expoxy from Alumalite. Poured about 3/4” thick and it turned out great. Just remember, you just have one chance with epoxy. If you haven’t used this material before you might consider a test pour. You must mix the two parts really well.