Lots of guessing , i can't do it.

Ditto.

Next time try using less single squares, and test your hanjie before you submit it. I always have to tweak mine. Good luck:-)

I got it first try by using some basic educated guessing.

Hints: (r,c)
1) A 2-length square in the center,
2) A diagonal from (3,3) to (7,7),
3) A diagonal from (11,3) to (3,11) &
4) An "X": [4,(15,17], (5,16), [6,(15,17)].

Use diagonal symmetry for the rest.

Sorry!!! Correction:
4) An "X": [4,(15,17)], (5,16), [6,(15,17)].

Thank you very much for the tips.