I chipped out a hole in basement floor and found the capped drain line. I cut the line to fit the p trap and started digging to make room for it and the toilet drain line is right below where the p trap needs to go. I have no sewer gas smell (line been cut open a few days now) and ran a snake in line and it makes a bend about 3 feet away. It feels harder to get through than just one elbow but hard to tell. Is it possible they put a p trap in further back under the slab a ran a horizontal line to where the tub drain would be? Is there a way to check? Thanks for any help!!

Is it possible they put a p trap in further back under the slab a ran a horizontal line to where the tub drain would be? Is there a way to check Very doubtful! That would make it a running trap and it wouldn't make any sense to put a job in that way. Hey! You're in a basement where you can move walls at will. So move some walls to accep the tub. The average tub roughs in at about 15 1/2" off the side wall and 1 1/2" off the front plate. All measures are to the center.
Good luck, Tom