Wire feed is not to hard in low heat setting . If the gun is trying to push back turn down wire if its arcing on and off turn it up . Do this in slight increments . When welding sheet metal do this at a 45 degree angle to work , this will stop the wire from pushing thru your weld .

As Dave has said sheet metal is just tacks building it up and filling in seem takes a while . Need to tack in some let it cool then come back and fill some more . Again as he said practice on some scrap while adjusting settings of temp and wire feed .