Buy fenders that fit, without bending. The fenders that do not fit were cast, pressed, molded, and/or extruded to a given shape. If you try to reshape them, they will possibly break. Too, if part of the fender can be reshaped, the rest likely cannot be similarly reshaped. The result will be a crooked mess. Reshaping the fenders may be a cost issue. However, your safety should have a higher price tag than the immediate cost. When the reshaped fenders break (which they are likely to do) you run the risk of the supporting rods getting wrapped up in the spokes. This is a fancy way of saying you will crash and the wheel will need work (IF it can be fixed. Be safe, buy stuff that fits.