I have an exterior door I am replacing. When the old door is out, the rough opening will be 33.5" wide. A standard 32" door calls for 34.5. What can I do?

I wanted to upgrade our outdated entry door with a new prehung entry door from Lowes or Home Depot. I'm a newer home owner with little construction experience but I like to get my hands dirty. I have replaced our windows with new prehung windows so I figured this project would be similar...

1. I have an original 1971 exterior door on the side of my garage I need to replace. The door width is 30" which means it's not stocked at the big box stores so I have to order custom. I decided to go with a pre-hung. When I got a quote for the order, I noticed he put "slab width: 30" but later...