Have you paid?
Have you asked the seller if you can cancel?
A sensible seller would accept your cancellation request but, if the seller says no and you have paid, you will have to wait until you get the item and then open a return through Ebay.
As long as you start your return through Ebay, and use the reason 'item not as described', the seller will have to pay for a label to get the item back and will have to refund you in full.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)