I found when I was struggling with U-turns on my gixxer (probably one of the worst bikes to learn slow riding / U-turns on)
I would stop about half a metre out from the u-turn kerb/line (at an angle) pointed towards the outside of the line/kerb then I would pull off aiming towards the line - I would then turn-in quickly without going onto full lock (full lock on a gixxer only has one result).
Maintain speed with clutch only (keeping the revs reasonably high). I can now get the u-turn in with about 2 metres to spare.
And as a footnote - never use the front brake on a u-turn
If you have to use the brake dab your rear brake only.
