I am going to give you my honest opinion whether you want it or not. It's not the weapons handling, it's a confidence and anxiety problem. When I did my BMQ, I had issues like that with weapons handling etc. I was so worried about "messing up" that my worrying would detract from the actual drills. Fortunately, I had better MCpl's that were able to explain that to me. I moved on and passed the test the first time, and went onto other weapons on other courses.
Looking back, it was not so much an experience issue as a confidence issue. Most people on basic have never used a C7 or anything like it before. Most people on SQ etc have never seen a grenade or a machine gun. The military has a history of teaching people (many of them probably not half as bright as you) to handle weapons. The drills are all broken down, taught and re-taught. A lack of confidence and a high level of anxiety can undermine the efforts to train you though, so definitely work on that. Learn to relax etc. I know it probably sucks reading that, but I have had to learn to overcome similar issues.
I wouldn't bother buying an AR 15 or something like that, unless you TRULY want one. Don't do it just because you think it will make you pass a course. In many positions in the CF, you hardly ever see a C7. Think about it, if you were an Inf O posted into some staff position, how often do you think you get to conduct weapons handling? Pretty much every range I have been on kicks off with a review of C7 (or whatever weapon) TOETs. This is regardless of whether you are excellent at your drills or absolute junk. But hey, if you really want to spend your money and enjoy shooting, go for it. Just remember that being able to do a drill at home with your own weapon is useless if you can't show up to work and execute it properly in front of a MCpl. Weapons handling is important, don't get me wrong. But in your career, you are going to mess up. Everyone does at some point. I have...in way bigger ways than failing a C7 handling test at basic, trust me on that. You have to be willing to mess up some times in order to learn and succeed.
I would take some time to consider what you want to do in life, and work on any personal issues you can. There is no reason to give up. You are not the first to have a setback in your career, and you won't be the last. If you really want to be an Officer in the CF, I am sure you can do it. I am sorry that it doesn't seem like you had the best backing from the CoC, but it is what it is. Maybe if in a few years time you re-join and go RegF, I will be your MCpl teaching you at basic. I wouldn't mind staying late or coming in at night to help someone, and I am sure there are more than a few instructors like that out there. You just have to bring the confidence and attitude, and I am sure you can do it dude.
Good luck.
(and Redeye has beat me to it)