You are shooting good especially for a beginner. Dry firing is great. Just make sure the gun is unloaded! When I dry fire I make sure ammo is out of the area as well as any loaded mags.
I see talk about the 21 foot "rule". If memory serves Sgt. Dennis Tueller came up with that. He was with Salt Lake City PD. He asked since we as police commonly train at 7 yards, how fast can someone close that distance with a weapon. Surprising to many it's about 1.5 seconds for an average size adult. That's fast taking into account the officer or otherwise legally armed individual must think about what to do, move if necessary, draw, etc...Basically this drill proved that someone 20 or so feet away who is armed with a weapon such as a knife is definitely in a position to kill or seriously injure you. Also since we should all know that shot ain't dead even if we were able to get a shot on target with the assailant closing in, there is no guarantee you will stop them prior to them inflicting injury.
For handgun training I usually shoot from 1 yard back to 25.