I have developed the magento website and it works great. I'm getting all order emails and shipping going good.
Last week, a customer who visited our website placed an order and cancelled at the final step. That product's actual quantity is '1'.
After cancelling the order, the product inventory should be "In stock". But it's not changed. It viewed as "out of stock". I have marked Set Items' Status to be In Stock When Order is Cancelled "yes".
As you are using Payu money extension, once we click on "Back" button, it will cancel the order and stock status will not change from "Out of stock" to "in stock", so you can hide the "back" button In payment page and if customer dont want to pay the money he will close the payment pages.