Can I return my iPhone XR back and buy iPhone 11?

As KiltedTim has pointed out, you will not be able to simply return the phone. However, Apple does provide a Trade-in/GiveBack program so you can potentially make the transition less costly.

Ref: Apple GiveBack - Apple

Based on the current return policy, you have already exceed the time limitation.

If you want to upgrade to the new iPhone 11, there are 2 options for you.

The 1st thing is join the Apple trade in project. Regarding you have just buy your XR for less than 1 month, and the trade in price is not very reasonable, so this is not recommended.

Another option is selling you phone via other 3rd party channel and get a relatively higher price.Then you can purchase via Apple official site.

XOXO, Kardashian

No. Apple's return policy allows 14 days. After that, it's yours.

You are passed the 14 day return window for Apple. You can ask the store manager but I think the answer will be no.