All the large continents are near the equator and hence the relative size of Africa, Australia, North/South America, Asia is not affected much by the projection. Antarctica is big too, even though wildly exaggerated by Mercator.
If anything, it makes more sense to say people don't realize how small UK/Europe is.
And I wouldn't call 29.6 <> 21.3 a little smaller, Africa is 39% bigger than North America.
Don't worry; Americans assume as a matter of course that England includes Scotland. Your internal political divisions are of interest only to you.
The widget also appears to include Northern Ireland, which, unlike Scotland, Americans probably wouldn't expect.