On my first shopping via bitcoin I get "The fee for this transaction seems unusually high. (20%)" What to do about it?
This is expected, given the current mempool situation.
There are over 100k transactions pending as of this answer's writing. This has resulted in the fees rising significantly, up to 10x of what you might pay normally.
As your overall transaction value is small, this results in the warning showing up. The warning itself was added to prevent people from paying absurdly large fees. In your case, as the amount is small, the fee is proportionally considered large.