Hi Duy,
This is a great little photo, and I fully understand the effort you went to in making it.
Many years ago, when digital cameras were still in their infancy, I used a friend's DSLR to do something similar.
The difference for me was that I had a model lying on her back with her mouth open… and full of water. A makeup artist friend used an eye-dropper to send a drop of water, one drip at a time, into the models mouth. For me the challenge was to get the water droplet as it bounced back up from the mouth. A very similar idea… and again it took about 300 photos to get the shot. Three models almost drowned in the process too!! (just kidding)
Technically I think this image is great, but my suggestion now would be to look at a different way of presenting the same image. Rather than using the cute picture of the cartoon girl in the background… look at something more real to include. This might be a friend's face, a pet or a flower. Make this image connect with reality!
Aside from that, great effort.
Cheers, Anthony