The shower can't enter the toilet line without being vented first.
An easy fix would be to wye off for the lav, 2" on the shower side of the stack.
The shower would come off that vertical with a santee, and then the lav would continue up with 2" through the roof.
The lav trap arms over to it's location. You can go 42" with the trap arm in 1.5" and 60" with 2.0"
The lav/shower winds up venting the toilet.
The way you have it drawn, flushing the toilet will siphon the shower.