not enough foam for single fin box?

The tail of my board is too thin to properly fit a 10" single fin box. Its my first board and i didnt even consider that that might be a problem when i was shaping it.
The last 6 in or so are less than 1" thick. should i just route it out to the max depth until i can do the proper 1 in depth further up the board?
Because its my first shape and I've never owned a board like it before, Im not sure where i want the fin placement or fin size or i would just glass one on.