first if you are thinking of selling here, you need to read ALL of the rules...one of the rules is that you are not allowed to FISH for interest in your items prior to listing them...another is that the items have to be for quilting, so suiting fabric might be out.
If there is no selvage then you need to tear it find the grain and measure that way...you might have done borders with it and cut it down the length, so the width is not normal now!
to test for poly you can do the burn test...poly will ball up and make a sticky mess, cotton burns straight across and makes ashes...
where ever you list it, be sure to note that it is washed, if people are sensitive to smells they won't buy it!