The tool you used is called a slide hammer. The usual procedure to fix a dent is:
- straighten metal as close as possible
- sand the surface w/ 80 grit to bare unrusted metal
- Apply bondo so that extends well beyond repair
- Sand the bondo flat with a long board sander
- If surface is still not flat knock down high spots and fill low spots w/ more bondo and sand again
- Prime repair area
- Sand primer and painted surface w/ 220 or finer paper
- Top coat with paint


1954 GMC 1/2-ton Longbed
1971 Pontiac LeMans Sport