Measuring BCD & choosing right chainset
It looks like you have a crankset with non-removable chainrings. The 'bolts' you are measuring the geometry of are just screws holding the chainguard on. The chainrings appear to be pressed steel and attached at the crank axle.
It's much more likely the pressed steel rings are bent than the bottom bracket axle, so replacing the entire crank is possibly all you need to do. The bottom bracket bearings may also be in bad shape which would require that to be replaced also.
Single chainring cranks for a square taper bottom bracket are relatively cheap, but there different model cranks require a different axle length to achieve the correct chainline. Sometimes it's easier to buy a new crank and matching bottom bracket than mess with trying to figure out what axle length a crank needs.