You make not walk on your line of putt.

Rule 16-1
a. Touching Line of Putt
The line of putt must not be touched except:
(i) the player may remove loose impediments, provided he does not press anything down;
(ii) the player may place the club in front of the ball when addressing it, provided he does not press anything down;
(iii) in measuring - Rule 18-6;
(iv) in lifting the ball - Rule 16-1b;
(v) in pressing down a ball-marker;

Decision 16-1a/12
Q. A player walked on his line of putt. Did he incur a penalty for a breach of Rule 16-1a?

A. Yes, if he did so intentionally. No, if he did so accidentally and the act did not improve the line.