This probably occurred because the first attempt to charge your card failed. When your payment initially fails after being submitted more than once, but one goes through, we end up with just one completed order for you. Each time a failed attempt goes through, it puts a "pending" charge on your card. Basically, your bank is waiting for us to capture the money. Our site automatically captures the money when you input your information. The failed charge should fall off your account in 1 - 5 business days.
If your order went through twice, you should receive a confirmation for two separate orders. Reach out to our care team and we can provide you with additional assistance if you may have a duplicate order.