Remember in your other thread when I said Russian tortoises need very large habitats or else they keep trying to escape? And I said that if your tortoise doesn't climb the walls, dig in the corners, then it is probably ok with its habitat? Well, if your tortoise is on its back a lot, that means it is trying to climb the walls to escape. Your tortoise is NOT ok with its small enclosure. It needs a bigger one or it needs to be set up outside.
That's a really nice-sized habitat for your little Russian tortoise. A few more fake plants in there will make it even nicer. The tortoise may try to take a bite here and there, but will soon realize its not edible. And such a tiny bite of plastic won't harm the tortoise. Like Joanne said, it will pass right on through.