demo help small lava pit

Please I need help I have to jump a small
lava pit but have not been able to do it I have tried every thing wlking jump, running jump used the god mode everything what else can I do? Please I need help.
Is it because is the demo?????? And not the real game?????

running jump... keep trying, the demo goes on for quite some time from there. I read somewhere that the perfect distance to begin a running jump is measured by walking to edge, and taking a standing back jump - then hold down the shift and arrow, and alt at the edge.