As a new rider I am horrified at the service that you've received. It is their job to make you a bike that you can get on and ride, they should fix/help as required without complaint until you are happy.

I would be writing to Soma, assuming that the shop is an authorised dealer for them. Experiences like yours will be tarnishing the brand image, and they ought to care about that even if the store doesn't. I would be asking the store manager what they can do to make me happy - be that a refund or fixing things personally. Or, if I didn't want to go near the store again I'd be asking the cool printer-fixing-dude that you know to recommend somewhere great, taking the bike there and asking them to sort it. It may well work out cheaper than the loss on a refund. But of course if you feel uncomfortable with the frame size then refund might be better. Again, the Soma HQ may be able to do something here if you let them know directly.

Good luck sorting this out, it must be heartbreaking and infuriating, but hang in there - you really deserve a bike that you love as much as your beautiful mixte.