A couple of observations.
- It always pays off to have a design specification. Once you have that then you do the design to meet your specification.
- Notwithstanding the preceding point - I believe you could have produced a much simpler solution with DC excitation of the load cells. The AC excitation approach seems counter productive.
Attached is a schematic of a 5V DC excited bridge with 4-20mA output. Purely by way of example, the bridge is arbitrarily assumed to give ±36mV deviation for full a scale 4-20mA output. The 4mA condition would be for -36mV bridge output.