This may be a stupid question for you guys, but I'm in need of a material that I can use to mold a curved edging of a tank. The tank is wrapped in pond liner, and the curved edge will be on top of the pond liner. The edge will have a radius of 4 feet (but a half circle) with a height of 1' 2". Here is an image of what I'm talking about - https://prnt.sc/kviqyt

Were thinking of using some sort of silicon glue to glue it to the pond liner, though the seal itself does not need to be 100% water tight.