Impressive work, especially on such a budget and tight timeframe!
Can you comment on the presence of turbulence around the drone (which creates noise in the ultrasound spectrum) and the reflectivity of a mosquito (relative to the artifact that you used in the proof of concept). Your approach is sound for 3D scanning in general but I don't see how the SNR numbers add up for the purpose of chasing mosquitoes with a drone.
I have experience in 3D object tracking using ultrasound if you'd like to chat (LinkedIn or email).