Quoted from PinMonk:I agree that you should put the leg bolts in loosely and re-center the bracket, which should distribute some of the gap on both sides. Then tighten the leg bolts (without the legs on) and it should pull to the cab evenly when you put in the screws.
This 1000%. You should never install the brackets without leg bolts (and preferably the leg) on there. That fit needs to be perfect