Sorry to hear what you have done so far, and I know that you did not want to hear that. You have to build yourself a good base in order to start your driveway, if this is a 'new' driveway. I suggest digging it out 4-6 inches the entire length of the driveway, as in you have to start over. Get rid of the plastic (what was that for, weeds?), you won't be able to compact over that. Then lay in about 4 inches of crushed stone (1-2 inch) followed by a 2-3 inch layer of 57's (1/2-3/4 inch). Compact that, preferably rolling, you could try a compactor. If it settles in to much keep adding 57's until you get it where you want it. Over the years add a little gravel when needed, and vehicles driving over it should keep it compacted. Just my suggestion.