When I do a new shower, I replace the P trap too, by cutting the concrete and removing the old trap.
I bring up the drain to fit in the new pan flange and install a thick gasket like: Jones Stephens Gasket to Make 2" Shower/Floor Drain No Caulk - available in plumbing stores - to seal the flange. This way I know it's done to code.
This brand is not the only brand around.
You must do things correctly to avoid future troubles.
Depending on your ability, if you doubt you can do it, get a pro.