Not cleaning off the goo as soon as possible makes the situation worse. If the bug juice has eaten into the protective layer on the 'glass' you will probably not be able to clear up the spot. I would take the canvas down and while laying flat, apply a concentrated solution of mild soap ( like boat soap) and warm water. (Try the solution in a less obvious spot first to see if it leaves a mark).
Let the solution sit fora while and keep the spot damp. Try 5 minutes to start without rubbing. Rinse and see how that works. It it helps you may need to do more treatments. Next tray rubbing with the solution and a soft cloth. Hopefully the stain will dissolve. Avoid anything with a petroleum base, that will harm the protective layer.
If all else fails, you can try an eisenglass cleaner/restorer and polish and hope for the best