Butt Welding 18 Gage w/MIG?

I have figured out the slow and patient part of this already, and I'm not really burning through any longer. But it seems like my tacks are up on the top of the metal and not really filling in the whole gap all the way down to the bottom of the metal. Do I have to tack it and grind it from both sides to fill in the gap completely and get a good cosmetic result?

dartlover