Open in OpenSCAD set your parameters, compile it, ..., export as stl file. Then skeinforge it as regular object (without raft ... otherwise its useless). You should stop printing after outline of first layer is done, printing whole object is waste of time and fillament. After print you can examine the bed by looking how wide is outline wall printed. It should be as consistent as possible.

In parts where the wall is wider is the bed little higher, and if the fillaments just sits on the bed, there is it lower.