It is not unusual for airtrack to need a regulation of pressure. In particular, when using it outdoors, you may need to adjust the pressure several times a day. This is not because it is leaking; it is simply a law of nature (hot air takes up more space than cold air).
For example, if you pump up your airtrack in cloudy weather, the pressure will rise if the sun comes out. The reverse is also true – the airtrack will lose pressure if pumped up in the sunshine and then the sun goes away. This may seem a lot when going from a hot summer day to a cool night, so don’t worry that it’s leaking – it isn’t.
If the airtrack loses an unusually high amount of pressure the problem is with the valve and it being too loose. Try to fasten it as tight as possible with the valve tool which came with the repair kit.