Well I'm not a plumber but you better get this checked out. On your drawing the W/C on the left and shower drain I believe is wrong. You show the shower drain on top of the w/c vent. You do show a separate vent for the shower which looks OK but the line drains into the W/C vent. If you're doing this yourself, go to a plumber supply house and asked them. A good chance the man behind the counter, or at least a customer at the counter, is a licensed plumber. The big box home centers might have a retired licensed plumber working the isles but it's doubtful.