It is virtually impossible for us to charge your card twice. What you are probably seeing is multiple pending authorizations. This is the case when there was any problem during the checkout process or your transaction was declined.
These are not actual charges. They are authorizations. We cannot charge your card until an order is completed. An order is not complete unless you are forwarded to an order confirmation screen where an order number is displayed.
The pending authorization will drop off after a few days depending on your bank policy. You can call them to verify this.