how to fix mansfield tolilet 106?

Hi
the toilet lever was broken, bought a new lever from lowes for the toilet. Now after fixing it, the valve in the toilet tank would not close, in order to close I would have to bring the nob up by hand to close the valve in the toilet, Is there any solution to this problem and also the lever locknut is stuck in the toilet and cannot make it loose to take it out, any solution for this problem.