Should the Clear Correct aligner trays fit snugly to the teeth and gums to be effective?

In order to understand how clear aligners work, you should realize that when you change into a new set of aligners, the aligners are in the shape that your teeth are going to BE, not the shape that the teeth presently are. Therefore, depending on which direction each tooth is being moved, you may see gaps between the tooth and the aligner. All this indicates is that at the end of the 2-3 weeks, your tooth will have been "pushed" into the empty space of the gap. At the end on the 2-3 weeks, you will see that the gaps have diminished or disappeared. Good luck!

I have been treating patients with invisalign for many many years.  Don't worry about the "gap" between the upper tray and the gum tissue. The most important thing is to make sure you wear the trays at all times, with the exception of eating and drinking.

You may want to consult with your dentist and discuss using some "chewies". These help to adapt the aligners to the teeth.