As others have pointed out, the name seems too much like Easteros (which would be a meme variant of Westeros from GoT), and it looks literally like Great Britain.

Even if not the map itself, the naming conventions would still give it away.

Maersa = Mercia

Lussex = not sure what the Lus is for, but the "sex" part in Essex / Wessex / etc. were used because it was Saxon territory, is it named like this because of similar reasons?

Scothos = Scotland

Brithos = British / reference to Brythonic languages

Irex = Ireland

Erumstaed at least sounds creative, first thing that comes to mind is irish -> erish -> erum + stǫð, so its some creative work

Sirumstaed on the other hand sounds like its just "Southern erumstaed", but merged together.

Anyway, you still deserve praise for putting the time and effort into creating this world. Hopefully considering some of the constructive criticism here will help in improving it.