Printer goes beyond the bed when auto leveling
I don't know how your firmware load handles G29 ,but here's a guess, based on information at the  reprap wiki .  Try using FBLR to force the travel limits. 


  Parameters
  
  P Set the size of the grid that will be probed (P x P
  points). Not supported by non-linear delta printer bed leveling. 
  Example: G29 P4 S Set the XY travel speed between probe points (in
  units/min)
  D Dry-Run mode. Just evaluate the bed Topology - Don't
  apply or clean the rotation Matrix. Useful to check the topology after
  a first run of G29.
  V Set the verbose level (0-4). Example: G29 V3
  T
  Generate a Bed Topology Report. Example: G29 P5 T for a detailed
  report. This is useful for manual bed leveling and finding flaws in
  the bed (to assist with part placement). Not supported by non-linear
  delta printer bed leveling.
  F Set the Front limit of the probing grid
  B Set the Back limit of the probing grid.
     L Set the Left limit of the
  probing grid
  R Set the Right limit of the probing grid