Not eating before bed is a myth. the problem with eating later in the evening, is because most people will make UNHEALTHY choices as they get tired. they look for comfort, and often they are likely not hungry at all just bored sitting in front of the TV

if you had done a spin class, it is very important to replenish your body within 20-30 minutes of your class. Depending on when you go to bed after wards, you can have a small meal with some carbs, protein and fat. a smoothie is pretty good. it depends if you had a dinner before.

this means you might have to reschedule your eating for the day, so that you are eating some kind of small meal around 4 PM (i assume your class is at 7?) so you aren't famished at 8 PM. remember your body expects food every 4 hours. other wise you go into starvation mode and your body will start to store everything.