If the stock stays flat, the value of your option decreases every day as the expiry date gets closer. This is because an option's value includes a time component - the longer there is until expiry, the more opportunity the stock has to move in your direction. As that time runs out, so does part of the option's value.
This time decay is one of the most important things to understand about options. It is why even a flat stock can result in a loss on an option position.