Can I know which payment method are you using? If you're using PayPal, make sure to turn on Auto Return. This usually happens when the user doesn't come back to the site from the payment page.
If you're using any other payment method, enable this option in those too.
To update this order, go to sellacious backend > Shop > Orders. Filter the order with Order Placed status and update the status as you want.
I hope this helps.