Assuming that you should be playing that chord at all (doesn't the backing track have it?), it's entirely up to you and your sense of musicality not only in what octave you play it, but also in what inversion, and whether you want to play it as an arpeggio - and then what arpeggio, because it doesn't just have to be D-F#-A-C in that order. You could play it, for example, as (1/4)D-F#-A-C, or (1/4)D-F#-(1/8)A-C-D-F#, or (1/4)D-F#-(1/8)-A-C-A-C etc. Whatever sounds good and doesn't detract from the melody should work.
Remember that this is music, and you'll be judged by musicians: a reasonable, musically appropriate creative effort goes some way towards demonstrating your ability. Whatever own interpretative element you apply must be musically sound, i.e. must harmonize with the melody without overwhelming it, be separated from the melody appropriately, etc. You should be able to write some ideas down and play them for your teacher and ask for feedback!