It comes down to translator taste with these kinds of things a lot. The general meaning is the same either way you say it in English, since it more or less is used that way in Japanese. That is to say, the distinction between "what am I doing?" in this specific context and "somehow" are similar enough to each other for both to be a "correct" translation from Japanese. In this case, they seemed to take a slightly more self depreciating "what am I doing?" approach to the translation, which I think is probably to suit the mood of the song better