Were you not using the middle wire divider in the double CN with the ramp closed? I'm not understanding how the rat chewed through the plastic tray and got through the wire divider.
A week and a half is too early for signs of possible pregnancy. You'll see a bulging belly a closer to 14 days and later. You can also do daily body weights to see if the rat is gaining weight. if you see a bulging belly and / or weight gain, I'd separate all of the girls into their own separate cage away from the boys and wait for the litter. I would not put the girls back into the original double CN even if you fix the tray / divider issue. You could neuter all of the males but that's kind of expensive.
