I have just recently been able to get my horse to do a collected trot, it is stunning to watch him do it and it feels like he's floating, but he can only do it for a few strides. Horses need a lot of time to be able to build up to it, its hard! You as a rider need to be fit enough to be able to get him there as well, it takes an incredibly amount of core strength to get a horse into collection. Get your main gaits down, a strong walk is imperative. A loose, working and slow impulsion filled trot goes a long way. Working to control a canter from a sitting trot will help you, but you have to be sure your horse is physically fit enough to preform these moves properly.
Talk to your trainer about your goals :) You will get there!