If you see a pending transaction on your account, but didn't receive an order confirmation, your order was not successfully placed. You can read more into why your order may not have been placed successfully here.
The pending transaction is only an authorization. An authorization is not a withdrawal, but rather, a temporary hold of your funds.
If an order is not placed successfully, any pending authorization(s) will typically drop off in 3-5 business days for US-based cards or 30 days for all other cards. However, this is dependent upon your bank.
Note that there is no need to take any additional action. All pending authorizations will automatically be removed from your account, according to your bank's policies.