Prince is "not" misinformed. As long as I've been riding, (20 years), if you had a round head, you went Shoei. You had a jar-head, you went Arai. Bell was somewhere in the middle. Here is proof of my experience:
http://www.google.com/search?q=Arai narrow head
It is true that both manufacturers are working on correcting that, and it is true that it started after the RF-900 (2008?) Why either would target one head shape or the other for so many years and lose market-share is not good business. There are so many new helmet manufacturers coming into the market now that will address "all" head shapes, that Arai and Shoei have had to join in, or get left behind. They should develop a colour-coded standard for head shapes.
OP, how long did the store clerk spend with you fitting this helmet. Do you still have the receipt? Hurting the sides of your head, and "chipmunk" cheeks, the helmet is too narrow at the top, and squishing your cheeks its clear that overall it's too small. What part of the GTA are you in? My suggestion: take the lid back with someone who knows what they're doing, and isn't afraid to scream a bit. Seeing you're a chick the leg-humpers on here will be more than glad to help you get it exchanged. I'm not a leg-humper, but if no one in your area volunteers, PM me, and I'll go with you to get the lid exchanged for something that fits. A helmet should "never" fit like a medieval torture device.