It's just too cold. Lots of guys cast just fine on a gas burner though. It's just a matter of finding your temp. It looks like you're gonna have to get it hotter though. Also, heating the mold more will help too. Some guys dip the corner of the mold into the melt to get the mold hot before they start. I don't know how to do that, I use a hotplate. But even with nice hot lead, a cool mold will make it puddle up and wrinkle in the cavity like that, for a while. If the lead is hot enough, it will eventually get the mold hot anyway and after 10-15 pours, you should be getting keepers.
'Looks like you are almost there though!
