I'd suggest to avoid spanish names with accents, even more those with ñ. I love my ñ, but it sucks when it comes to reg domains, you always end up registering something that is both ugly and wrong.
Gran Bretaña is right and sounds right, Gran Bretana looks bad and sounds bad. The IDN might be right, but IDNs are browser-translated into punycode, which sucks by itself...
Get rid of it.