Creating a map with only RPLiDAR A2

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So I am trying to create a 2D map on RViz with only an RPLiDAR A2. I am able to successfully get the LiDAR to turn on and I can see the red laser scans in RViz following this guide: http://wiki.ros.org/rplidar. I also did a "sudo apt-get install ros-melodic-gmapping ". After I ran in a separate terminal "rosrun gmapping slam_gmapping". I changed my fixed frame to map as well as added the map from topic list.

I am getting an error in that map no is received. I am not sure how to fix this issue, i'd like to just walk around my room with the LiDAR in my hand with my laptop to map the room.