This is a very good melody for a first song, actually!
But that's kind of the problem, it is mostly just a melody. (with some hi-hats added)
This makes the song not be catchy and feel pretty much empty.
I would recommend you try adding chords and a bass to make a "full-er" song. You could also try to add counter-melodies, but I would stick with chords and bass first!
Also, it is nice you added drums, but they aren't really hearable and it's mostly just hi-hats. Try to add kicks and snares to make a more composed rythym.
Still, it's nicely done!
Edit: I see, I do understand that!
Try to start with the bass or the chords and NOT with the melody, since it is a lot harder to make some good chords or bass from just a melody instead of the contrary.