i made the previous circuit PCB everything seems work fine and stable
but the bad news is using 20R in parallel with 100R VR didn't make the bridge balanced
i found out that it can be either 50mv or -50mv and can't reach less than that which also doesn't show any output change after amplification
so any suggestion??

 

i have another questions

using OP07 instead of LM358,would be better??