You should insist on getting information from your dealer:
1) for 2020, the number of allocations received...so how many 2020 C8's did they actually put in customers' hands
2) for 2021, the number of allocations received to date (how many 2021 C8's delivered to customers) and what they're expecting to receive for for the remainder of the year (usually it's a close match to what they got in 2020, although there's no "guarantees" so that's an approximate but fairly useful assumption)
3) confirmation of your placement on their list: exactly what number you are now and whether all those originally in front of you received a C8...or did some drop off the list for various reasons and bump you up as a result (find out how many dropped off)
4) #3 assumes that once someone drops off the list, you'll automatically move up the list. But get confirmation of this as well. Some dealers will take allocations from customers that no longer want them and order the car for the dealership itself and sell it at a profit. I'd recommend NOT staying on the list with a dealer who does that.
I don't know anything about Carters GM and perhaps there are other members of these Forums that do and can offer you more precise advice. At least you know you're not paying over MSRP...and many dealers will add on an admin or similar fee, so that's not unusual.
Talk to your salesman and if he's not helpful, then meet with the sales manager of your dealership to get the above info. If you don't get answers to the above, I'd move on: pull your deposit (or leave it there if small enough and you're not concerned about it sitting until you get a C8 from someone else; I assume your deposit is refundable until the order is placed; it should be) and find another dealer who gets a good number of allocations and you'll have a better chance of finding a C8...or at least hopefully you'll be better informed. To find that dealer(s), ask around about different dealers and look up Web reviews about those dealerships and when satisfied you've targeted a couple that are good (ensure they're into Corvettes), call them to get their allocation experience and see if you're comfortable with them and then sign up with one or both. And yes, going to the dealers that are sponsors here is a good idea although they're in Ontario and I see you're in BC. You'll pay an extra $1,000+ for shipping, if you buy from Ontario. PM (private message) me on these Forums and I can give you some dealer options for the Edmonton and Calgary areas as well, if interested. I know some members from BC who purchased their C8's in Alberta and picked them up here and drove them back to BC, avoiding ship costs and they had a fun drive home with their new car.
If you really want to get a C8 you'll need to do your "due diligence" by asking around and choosing the right dealer but that effort should pay off. Or maybe Carters GM will come around and satisfy you by answering the above questions to your satisfaction...
Unfortunately if you're now #15 on the list, it's unlikely you'll see a 2021. But if you don't want to be in the same boat for a 2022, I think you need to do the above. Good luck! And as I said, contact me and I'll see what other advice I can offer.