Help - Surface creating issue (cannot fill a gap)

Hi again, I don't like to ask to many things but I'm strugling for about 3 hours and I cannot get it to work

My problem is in filling this gap (below) for molding creation (don't know if it gonna work with the fill system but i need a mold with that

Can somebody help me out with this, I'm out of my mind with this piece of s*

thank you in advance

SolidworksPlastics And Mold Design