You might need a longer transition and a lower lip. that was my biggest problem after first building mine. Orange construction fence as said above is very good as well.
My setup was too slow when I first built it. Your ramp may me be too short or not steep enough but my solution was just to use poles and get a good push at the top of the ramp. This plus soap and water. I found that the orange fence didn't work much better personally. Give the poles a try.
If the angle between the ground and the drop in is to steep you will lose all your speed. It's is nice to have the dropin/ rail on a slight downslope just to keep speed! If it's flat your screwed, because you lose speed very quickly on summer set ups!