Don't get too obsessed with making into a perfect wedge at the start. Just pile it up then carve it out later on. If it's below 0 then a bit of water will help it freeze. Otherwise sprinkle a SMALL amount of salt over it.
Warm beer is infinitely colder than no beer
NS User 45. : "Your terrain park would be responsible for more deaths than Hitler."
First urban jump I made on campus I piled up a bunch of snow but I didn't have enough know-how to form the powder into a sturdy shape. Do I dove in a dumpster, emptied all the trash out of a bag, shoveled nasty ass creek water into the bag, and made the jump. Take initiative with you resources/brain.
Here is a real answer for you. Grab a piece of plywood the wider and taller the better. Jam this into the snow and shovel the pile of snow you have into this piece of plywood. This will now act as the back of your jump. Pile it high and wide, if you have more plywood use it for the sides of the jump. Pack it all down into the desired size and shape. Hope this helps.