On Wednesday, June 8, 2016 at 2:26:47 AM UTC-4, wrote:
What are you using to create the V-groove in the plexiglass?

I repaired a good number of cracks in canopies over the years and use a Dremel-type tool with a small end-mill. That tool cuts on the side and the flat front. Holding it at 45deg., the groove will have a 90deg opening.
Cover the crack with one or two layers of strong, clear packaging tape and work through these layers. You WILL slip with that tool and the layers of tape prevent any tool marks where you don't want them.
I use the '192' premixed cement rather than the two-part stuff.

Uli