I made a boo boo... I ordered a 20 x 30 of one of my images (1" gallery wrap on canvas) but I didn't proof it first

I had the profile for the printer that they used to print it. I just forgot to hit CTRL-Y and make sure it looked ok first. Bummer.
I'm not posting here just to whine... It occured to me after I proofed it that I didn't have a clue what to do to make it print right... that was my first print and it sucked. My monitor is calibrated and the image on the monitor was exactly like I wanted it to look. When I hit CTRL-Y the image goes flat. I can't post it like that. It's got way too much contrast. It perfectly matches the image that is on the canvas... but in my opinion that image sucks (my son loves it so I gave it to him)... My little pea brain doesnt know what to do with the image. Do I tweak it in Proof mode? If so at what point do I do that? I edit in 16 bit ProPhoto RGB space (I'm not changing so don't waste your time arguing with me about it). Then, since the printer that I used (grumble grumble) REQUIRES JPG images (much to my dismay), I convert to 8 bit and Adobe Raw and then do a Save As JPG. In this case I can't blame the printer. I screwed up and I chose to go with a teensy weensy (in my opinion) JPG so they did exactly what I asked them to do. I need some help with this part of my workflow...