I'll throw this link in here so this thread doesn't turn out to be bad.
Critical and picky - here I go again
Even though i've not had much experience using Plexi-glass in robot operations, I've played with it enough to know that it will shatter and crack fairly easily. I also seem to remember a lot of threads in the past asking this exact same question, "Should we use plexi-glass or lexan" and the majority of the time most responses went, "Use lexan" for one reason or another.
Also, one thing i saw was people confusing the terms lexan(polycarbonate) and plexi-glass(acrylic). I just don't want this thread to turn into a "Let's argue about what its called thread".
This is not the end of the world for your robot. With the right support I think it will be just fine, but that's just my opinion.