Nothing wrong. (I know, it's six months since you wrote the above, but in case anyone else arrives at this sentence with questions about it I'll answer anyway.)
іти is not only "to go", but can be translated as "to walk" or "to go on foot".
In lesson 1 of Verbs of Motion we are introduced to іти and їхати both of which mean "to go", but іти is by foot and їхати by transport.
From what you've written you probably wrote a correct translation, but not every possible translation is in Duolingo's list yet. Duolingo builds its list of correct translations over time as people report them for not being accepted. The course contributors can only guess so many ways of writing things in advance, and there are always missing possible translations in any language course on a computer - computers aren't quite clever enough yet to infer correctness. When a translation is not yet in the list it is marked as wrong (unfortunately even when it is right) and a possible correct answer is shown.