Inaccurate Gmapping Map with Gazebo 8 and ROS Kinetic

[MsMimi]

I installed gazebo8 and ros kinetic as the instructions from https://medium.com/@abhiksingla10/setting-up-ros-kinetic-and-gazebo-8-or-9-70f2231af21a. I need gazebo 8 since Im using VMware Fusion on MacBook. Next I install most of turtlebot packages using apt-get, while turtlebot_simulator, kobuki_desktop, and kobuki_msgs from source.

When I try to run turtlebot_gazebo gmapping demo and visualize in Rviz, the map result is not correct, it creates a lot of obstacles where there is none. I'm quite new to ROS, at first I thought it was installation program, so I remove all ROS, Gazebo etc and repeat the installation, but the same problem still occur.

Attach is the simulation world and rviz map.

Thanks!