I would want more aeration in there if you are going to use the peat. Peat is an awesome product but to use it you need something in there to break it up some. Even some lava rock, hydroton, man anything to get some aeration in there would be good. I would like to say you could chance it but I would hate to see you have problems after spending that money on everything. Any chance it can wait till tomorrow morning to give you an opportunity to find something? I bet you could even find styrofoam in the dumpster behind walmart for free. If you told them you needed a chunk to work on some project for your wife or kids school project there would be no questions asked.