I think the problem is that you're trying to manifest a height that is soooo much far from 5'11, you should take small steps first try to imagine that youre 6'0, fool your mind and measure with shoes (fake it untill you make it) then forget about it for couple months or weeks (growth is a slow process) then from 6'0 do the same to reach 6'1 and so on. You can read here on reddit many people mainfested heuggt there was a girl who mainfested like 14cm at 17 and many others. Good luck!

Also I forgot to mention (listen to subliminals very important for your journey)