By D3/38 I mean the specific note that will cause that note to play in the game (the left normal note in that case). D3 means it's the D in the 4th octave, since octaves start in 0 (in FL Studio at least, I think some DAWs actually do start from 1, so for those you have to move all the notes up an octave, so D4, but you're using FL so ignore that lol). The number, 38 in this case, means the internal representation of the note, since computers recognise the notes as just numbers rather than their proper, more human readable names.
If you can't find it, try importing the midi of the copy of Raise Up Your Bat map that's included in the custom maps folder into FL Studio, that will let you see the correct placements.