i thought i was talking my time to let it cool between tacks but no . ended up with a sink hole. how do i go about pulling this up and getting it to stay .
The weld pulls together as it cools - Fast or slow doesn't matter too much. It pulls much like the jaws of shrinker do. To reverse or correct that pull at this point you need to stretch the weld back out by hammer on dolly over the weld and decreasing the stretch as it reaches the end of the heat effected zone. You could have tapped on each of the tacks as they were fresh & hot and it would have controlled and minimized or nearly eliminated any movement in the panel. For hammer on dolly to work the back side of the panel needs to be clean & free of weld bumps (smooth) & backed up solidly with a dolly. It usually doesn't take too much to correct it. It's very easy to over stretch the area or parts of the area and that's where the shrinking disc really shines. As counter intuitive as is seems, tapping down on the panel with on dolly backup will raise the place you're hammering.
Close to 30 years ago I took an old school body man who was a customer / pal, an ot fender with same problem & witnessed him using an oxy actelene torch with a "rosebud" and the ol wet towel trick in increments & the lump went from a 1/4 inch to zero. No body filler necessary. Man I love'd watching old school body men & their tricks. Flux
31 Vicky is absolutly correct. Do Not start hammering on your low spot. There is a term called Hammer Welding, do a Google search and watch some video. It's really quite simple once you get the hang of it. Like all things you can over do it and cause a new issue so go lightly till you get the grasp of it. Something that helps prevent what you have going on is NO Gap seams. Using a wire feed welder seems to add to creating your problem. Gas or Tig is a better choice in my opinion. The Wizzard