Every time I try to bend the face of the fender to the car body, I get these weird bumps?
The surface is uneven, because the vertices are arranged in such a way, that the faces are bent. You can fix this by manually adjusting all the vertices to create the cleanest shape possible.
You can try and clean up your mesh, by going through all the vertices, and adjusting them manually from each angle. This can take more than one pass.
It will be easier if you use cleaner topology. When modeling with quads, it is advisable to make the faces as even and as square as possible.
You can achieve more even quads, by deleting some existing edge loops, which aren't necessary for the shape and add edge loops perpendicular to the previous.
With Subdivided Surfaces, you only need four vertices for a cirle. Keep topology rich in information, low in detail.