Well liq the first thing is make sure you're using the right string. They wouldn't make variously weighted strings if any string could be used anywhere. Make sure you haven't put in a G string where you need a B.
Next when you tie up the string at the headstock make sure you don't put it in the rotor so deep that there's hardly space for the string to expand. Turn it around a few times first. (hope you're using an acoustic?)
Next confirm your tuner for disturbance (happens). Try comparing your B note to a keyboard or something (or use some damn MIDI program on your PC).
If nothing happens, well, keep tightening.
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