Help Fixing Shower Threshold

How bad is the slope? Like is it 1/8"? More or less? They make a type of threshold that you can put down to sort of dam the water back. They say they're 1/4" tall, but really they are closer to 3/16" tall. You can't order from that site I linked to as it's wholesale, but you can find resellers that have it. Some local glass shops might have them, too. I always keep some in stock.

Cut it to where it's tight against the wall and the side panel, and then apply a decent amount of silicone and stick it down. It also helps to dam up the sides a little bit. If your curb is made up of multiple tiles and not a single piece of stone, then there's a good chance you have grout lines that funnel water out under the sweep. Make sure the silicone you apply to that threshold insert seals up those grout lines.

You will never get it to keep from leaking, but you can slow it down. We've literally installed 1000's of shower enclosures, and every single one that had a mis-sloped curb has never not leaked. I always check them when I measure for the glass and let the homeowner/contractor know that it will leak and I will not warranty it for leaks.