I know why you've written it that way, because 'concentrarse' is a reflexive verb in Spanish. But no, that sentence is not correct. Correct: 'I need to concentrate on my homework' or 'I need to focus on my homework.' By the way, homework is uncountable. It is not possible to say 'a homework'.' You say: I'm doing my homework/I'm doing some homework.

I would nix the "myself."

Umm its not wrong but people would usually say "i need to concentrate doing my homework" instead :)

Well, because you already have the word 'I' in there the 'myself' is not needed.