For every Invisalign case, we give our patients a set of Invisalign retainers to wear just at night for the rest of their life. After spending money and time you do not want to go back and let your teeth shift. Wearing retainers every night is more than enough, it will protect your teeth also...
I am sorry to hear that you are having a problem but it is impossible for the tray to make an indentation on your tooth. The pressure would only cause the tooth to move. You make have an attachemnt that has been placed but not an indentation.
While it may seem odd, most cases need some form of space management. Sometimes teeth are extracted, but often just some polishing of sides of teeth is enough. This is true for both Invisalign and regular braces.