Yes, you would fall onto deck 9.
I would rely on the Princess website for deck plans.
I do not see C312 as an accessible cabin. It is possible that it’s not updated, but not likely.
You can check the box (wheelchair accessible) on the Caribe deck when you check availability in PCL website. For midship caribe, it shows these as accessible cabins.
Did they give you C302, perhaps?
Uncheck the box now and look at availability again. You will see laundrette is across from C612 & C615.
If they gave you a midship UG on the Caribe deck, that’s a nice UG. Don’t know about the accessibility issue though.
If you have a TA or CVP..please have them help you with this. Don’t rely on a PCL phone agent.