You have to keep in mind how fast the music goes by. The F sharp quickly resolves to G, so I would see the F sharp as a non-harmonic tone.
In fact, I would think of the first 4 measures as all being a C major chord, with an inner melodic line created by a series of non-harmonic tones, each of which quickly resolves to a chord tone.
Anyway, that's one way of looking at, and possibly the most useful way in terms of actually learning the piece.
You could, of course, also stop to analyze each chord quality along the way, and that might have some value too. In that case, I would like to think of the chord in question as a sort of polychord—meaning two chords sounding at the same time: C major and F sharp half-diminished seventh.
I think it sounds wrong to you because you're reading the piece slowly, not hearing how quickly those 32nd notes go by. Also, you have to hear that F sharp as a melody note (a repeat of the melody note in measure 2, in fact) not just as harmony.
Make sense?
