No worries, placing a duplicate order normally won't be an issue. Most of the times when people place duplicate orders, it's because they had problems checking out. Usually, payment only succeeded one of the orders. If that is the case, the other (unpaid-for) orders will simply be ignored by our system. You will not be charged again, and only the order that you actually paid for will be shipped. (should you receive any 'waiting for payment'-type reminders, you may ignore them)
If, however, you did pay for both orders, please notify us as soon as you realise the mistake. You can do this by opening a support ticket. As long as the order hasn't been prepared for shipping yet, we will probably be able to cancel it and refund the money. We do charge a €5 fee for cancelling orders that have already been paid for.
If you're not sure how many orders you actually ended up paying for, you can look this up in your Account Dashboard. An order that has been paid for already will have one of the following statuses: Paid; In Transit; Shipped; Waiting for Approval. An order that has not been paid for will usually have one of the following statuses: Waiting for Payment; Processing; Closed.