Measure current through H-bridge using shunt
The TL972 is not a very appropriate op-amp for this purpose. It requires a negative supply since the input common-mode range only gets to within 1.15V of the negative (or positive) rail (despite the output being rail-to-rail). You show the supply grounded, which isn't going to work (assuming the current is less than 115A!). 



It also can have as much as +/-6mV Vos which would represent an error of about +/-6% in your trip point- maybe that's okay for your purposes. 

Suggest you substitute a single-supply op-amp with a relatively low input offset voltage. Since the TL972 has a standard pinout for a dual op-amp that should not be difficult.