Where is the entrance to your room? It's definitely possible to do three concentric ovals in 11 x 20. But your benchwork would be of the "open doughnut" variety- a series of perimeter modules with an opening in the middle, that would have to be accessed by a lift gate, duck under, or swing-out section.
If the entrance to the room is on the right, I also think you could do a folded dogbone, with the turnback loops offset from each other. You wouldn't have very long runs though.
I strongly encourage you to think about other options. My train room is 11.5 x 18. After buying nothing but scale-sized trains for more than 10 years, I gave up on the idea of two concentric ovals. I'm afraid I'll get bored with it after only a short time.
