Alright. I'll try to help you. It's unbelievably easy.
First if all, the "invert" (interior bottom surface of a pipe) of the vent connection must be above the centerline of the drainage pipe to which it is connected. What this means is that your piping is all wrong.
Cut two inches upstream of the galvanized strap and throw all the piping away. Install a 2x1&1/2 PVC wye first, beginning where you cut. The branch of the wye, the 1&1/2 part, must be rolled up high, upper quadrant, because the vent is going to go over the top of the two inch drain pipe you're about to install.
Forget the vent for now. Install a short piece of two inch pipe into your wye to get you back to your original angle serving your p-trap created by using a two inch 45. Then a short piece of pipe over to your new glue joint adjustable p- trap, centered on your shower drain centerline.
Now your vent. Install an 1&1/2 street 45 into your wye branch aiming towards your vent wall. Your vent will cross over the top of your drain passing right by your shower drain riser and roll up in the same spot it is now or close.
One more thing. Your vent 90 rolling up in the wall, horizontal to vertical, must be an 1&1/2 LT 90. ( Long turn) because it is below flood rim.
Clear as mud. If anyone out there understands this and can help with an illustration...