IIRC, plexiglas is best worked wth a solent thing, not a glue. A chain around her, TAP Plastics, sells a 2 ozbottle of the solvent, alog with a really cool applicatr op for the bottle. The applicator is sort of like a hpodermic needle -- real thin and hollow inside, the solvent flows through it.
I have no idea what the solvent is....try a walk through yur local Yellow pages and look under plastics / plastic suppliers, and make a call.
Again, IIRC, MEK will also dthe trick, but I don't like messing with MEK and don't recommend it. The stuff from TAP Plastics that I use does not smell like MEK.