I'm not trying to pick fights (at all - please just tell me to knock it off if I'm being rude, again I'm not) but I find it strange that you never cantered yet bought a horse. I know a lot of people do that, but still.
Anyway, no one can really help you become a confident rider besides yourself and the horse. If you trust yourself, then good - you'll most likely trust the horse.
First thing to do is RELAX. Take a deep breath. Think of only positive things, and thinks you want to accomplish - not do wrong.
That's all I can really say - the rest is up to you.
It also helps to ride a good old school horse - that'll boost your confident up. Also, seeing someone else ride your horse helps, too. Good luck.