Hello out there and thanks for looking. I've been scouring the net looking for how to fold or cut corners for my membrane pan liner. I've already ruined 2 corners! My shower is an alcove style: 3 walls. The 2 back corners were easy as I had some space between studs to tuck the corners in but I'm at my wits end on how to do the corners by the curb. Im totally mystified. Ive seen what look like pre-made dam corners but don't know where to get them or how to make them. Please help, I'm stuck and frustrated...

Thanks.