ZBrushCentral

Noobasaurus rex question

Hey all, work ing on the skull tut and im at the very begining. Problem is that whenever i use a sketch brush to lay down a stroke i get a gap when i approach the axis lines when it snaps to the green center box if that makes sense. can anyone point me in the right direction to get past this super noob quandry.

You can’t sculpt evenly in the middle of the skiull - do I understand it corectly?
If so - If you are at the center of symetry, turn symetry off (X-key) to sculpt lines that won’t cross eachother.