Sure hope you're not leaving this corner like this.
A Maserati doesn't deserve this kind of repair.
Building a corner or edge with fiberglass will be a failure not long from now.
For this corner, you could take a piece of round rod to use as filler "patches". Cut about an 1/8 of the wire edge you see off square to the panel and tack a piece of rod with the same size radius as the rolled edge, If needed, another piece could be added on the other edge.
The rod is solid, so when done you could grind a nice radius on the corner and it would look factory.
Take you time and complete all your tacks. The bottom right gap can be filled. You're not taking you time to hold the wire aiming exactly at the crack between the two pieces. Rest the nozzle on the fender, then aim, then zap the trigger.
I use a zip cut disc, (a used, smaller diameter one) to carefully cut the proud off the welds without digging below the metal's surface.
Is that metal galvanized steel or some kind of plated metal? What's the coating?
If it is some kind of coated stee, you need to grind it off before welding as it will spit and spatter
Or, did you put weld thru primer before welding?
If so, you're using it wrong. It's used on overlapping pieces that you cannot get to after they are joined.
If you can get to the pieces, like a butt welded patch as you're doing, it's not needed.
You need to practice on scrap as mentioned.