Adobe Community Professional
Lightroom Queen and general geek
It might be that your mind is convinced that it can trust you system but your instinct is not to. To truly trust your system is a habit change - and how hard it is to change your previous habits depends on how deep they have been engrained.
So in addition to looking at your present GTD implementation for any gaps in the actual system, it might also help to observe and try to work out where your feelings of anxiety come from. Is there anything in your past? Can you pinpoint what specific contexts or events that trigger your insecurity? (no need to answer, just rhetorical questions...)
So I would suggest you focus on building trust in your system. Test it. Next time you capture something a second time... check... did my system really have it. If it did, remind yourself that you don't need to think of things a second time ... your system's go it. If it doesn't, ask yourself what your system needs to have to give you more confidence it's got it and it'll be there when you need it.
I think all the suggestions you've received are great. For me, building a regular weekly review + having a project around tweaking my system, is what really helped me build the trust. I think if you start with the weekly review and add a question to ask yourself each week "What can I do to rely on my system more?", you'll eventually get there.