Listen to all the advice and then find your own way and one that's comfortable for you. There's no way I could sit like some of the lads at the club because it's just to uncomfortable for me.
So, I've taken their advice and worked on what's comfortable for me and gives me the best stability. It's still far from perfect but I'm getting there. Only practice will make it better and yeah some days I have the same wobble problems but try not to over think it and just keep pushing on. Everyone has off days but with loads more practice, it will become automatic and you won't even have to think about it. I reckon you should get there in 3-6 months if you shoot twice a week.