Can I trade in my iPhone 17 for an iPhone 17 Pro?

Doesn't look like it. The Apple trade-in value website only goes up to 16 Pro Max.

https://www.apple.com/uk/shop/trade-in

If you bought the 17 less than 14 days ago you can return it for a refund.

How long have you had your iPhone 17? If no more than 2 weeks it can be returned to place of purchase in most cases. Did you buy from Apple or a third party? Have you talked to the merchant to determine if you can return or exchange your iPhone?

I do not believe that Apple accepts current models as trade-ins.