I also have that lens and yes, at 55mm the lens is almost coming off the threads. I’d suggest a few turns of Teflon tape around the threads to keep the lens from wobbling out of focus from machine vibrations. If you don’t like it this loose then you can always screw it in further but then your focus distance will increase too. There’s a trade-off here. Too close and you risk fouling the lens with smoke but if you get too far away, the beam power gets slightly diminished.
One way to focus: Set laser power to lowest possible setting where a beam spot barely appears, this is about fan speed=3 on my laser but every set-up is different. Adjust lens to focus beam to smallest spot size possible, a dark matte material tends to help make the spot more visible and less reflective. The spot size on the 3-element lens should be about .006 to .008 inches. At the lowest power level you won’t get burned and you’ll just be turning the knurled part of the lens so your fingers shouldn’t be in the beam anyway.