Buzzer,
In case Simon's reply is too cryptic, be aware that values passed to drawing commands in shape scripts (e.g. rectangle(), moveto(), lineto()) are percentage of the overall shape. So to create a 50x50 square, the following is wrong:
shape main
{
rectangle(0,0,50,50);
}Instead, you would need:
shape main
{
defsize(50,50);
rectangle(0,0,100,100);
}