Basement Shower

I am planning the development of my basement. I plan on installing a corner style shower base. My house has the plumbing roughed in. I asked for a 3-piece rough-in but I think I got a 2-piece? There is one pipe protruding from the concrete floor (which I assume is for the toilet) and there is one pipe protruding from the unfinished wall connected to vent stack (which I assume is for the sink drain). Can I connect my shower drain to the vent stack as opposed to breaking apart the concrete to connect to the below grade drain? I understand that I would need to raise the shower base to allow for the P-trap from the shower drain. Or is there a better alternative?

You may want to post a picture here of what you have.
You may have a drain for the shower under the slab already if you asked for one.
All plumbers would suggest breaking concrete and placing the shower pan on the floor.
Or you will face "falling" out of the shower for years.
I consider a raised shower pan or tub as a health hazard.

Thanks for the feedback. Upon further inspection, I did find the 3rd piece of my rough-in. It was located under a cover plate buried under gravel.