When you start hammering, do you still have little dents and such to fill in with bondo (just not as much bondo as you had before hammering)? I pounded on my hood a little and got the dent mostly straightened out, but still had to apply a little fiberglass (my choice rather than bondo) to make it flat.
Take an old fender and wack a dent into it. Then work it back out. There are many good books out there on this subject. Its more than just hammering out the dent. Metal stretches when its dented so you have to shrink it back, along with hammering out the dent. I'd go down to your local library and check out some books on metal working. Its facinating stuff.
