Filled Mini Cooper w/ reg unleaded. Is that a problem? on 2002 Mini Cooper

I just noticed premium unleaded info. I only did it once

Get Your Car Fixed at a RepairPal Certified Shop.
We certify shops based on expertise, quality work, and verified customer reviews
1 answer
That's what i told my wife but she didn't believe me!

Why do you think this might be a problem? Is premium fuel required or recommended in the owners manual, for the engine in your car?