Inaccurate sleep and nap tracking

One of the reasons I got a Garmin was to help track sleep, but honestly the sleep tracking is practically useless.

My Lily keeps recording me as napping when I'm sitting reading a book. Even worse, when I read in bed in the evening, the watch records it as me being in deep sleep! Not only that, it's the only deep sleep period that gets recorded - when I'm actually asleep, no deep sleep periods are recorded, regardless of how deeply I'm sleeping. It also records me as being in asleep when I'm actually awake in the morning and just haven't got up yet. 

This all completely throws off the sleep stats. The free sleep tracker app on my phone that I used before getting the Lily is more accurate, which is simply ridiculous.

Is there any way to improve the accuracy? Or to at least delete the 'naps' that are being recorded when I'm not actually napping?