Sorry to hear you're having difficulty.
Go into the booking system, click on My Calendar and check that it shows your reservation for the day and time you think it should be on. And have a look in Schedule Calendar as well; see if you can find your reservation there and check it thinks it is for the same day and time. Your chosen lab time and GMT setting should make the booking wrap over onto the next day and we need to check that's working okay.
It might also be worth making a booking for a day/time that won't cause the day wrap, just so you can get a handle on how the booking system works. It doesn't matter if you can't do the lab at the unearthly hour selected; just make a practice booking then cancel it again.
Finally, if you're still having trouble let us know the exact day and time you've booked for and we'll look into it