Check carefully around the base of the pipe; if you are lucky, the builder put a sleeve around the pipe you can dig out to allow you to put a normal flange on the outside of the pipe. Note, it might be covered just at the top by a thin layer of cement.
It is considered 'ok' to use an internal flange on a 4" pipe (although outside is better), most do not like to do it on a 3" pipe.
The flange needs to sit flat on the floor, with no space underneath and you need to anchor the rim to the concrete, otherwise an inadvertent knock on the toilet after installation could break the flange. Plus, if it sits higher than that, some toilets won't fit - they'll be held up by the flange, rock, and break the wax seal in addition to the flange.
You might be able to use an internal cutter to get the top of the pipe slightly below the surface to then allow the flange to set down flush with the floor.