"Shipping" can include time in the mailstream before delivery. So don't worry.
Mark Day 20 after purchase on your calendar.
If the item has not arrived from USA, Canada or Europe by then, contact the seller again and ask for the date of shipping, the service used and the Delivery Confirmation number.
If the item is coming from Asia, wait until Day 30.
If the item has not arrived by Day 40, contact the seller and ask for a refund. If he refuses (or offers a replacement) open an Item Not Recieved dispute before Day 45.
But at the moment, the item, if send on March 3, has been 14 business days and 20 calendar days in shipping, which is well within normal delivery parameters.
Chill.