By the looks of your picture you are using gargraves or Ross track over cork roadbed. The track is 1/2 inch high and another 1/4 inch for the cork. Allowing 1/2 inch minimum for the baseboard and at least 4 &1/2 inches for the train, you're at 5 &3/4 inches, not counting any kind of support for the base and air space for access.
You won't be able to get 2 turns of O-54 track into the space allotted. You can only get 1 turn no matter what radius. Try for a larger radius if you want a 2% grade or stay with O-54 and increase the grade to 4% or more .
Hope this helps.