I found a few problems:

F = n((W +(Wa)/2)/tan(theta))

I get F=2 n((W +(Wa)/2)/tan(theta))

1.When lift is collapsed (lets say angle is 5 degrees):

F = 2((25 + 7.5)/tan(5)) = ~149 lbs of force

I get 1400+ lbs.

5 degrees is too small;the price you pay for compactness.

Yes,scissor jacks are very inefficient at the start.