Students often complain that their low range isn't very good but when asked how often they work on it, most of the time, the answer is: " mmmm... never..."
If you want your low register to improve, you need to spend at least a few minutes every day playing some drills in the low range and some pieces in the low register. You can practice some low excerpts or play solo pieces an octave lower. It's a bit weird but it works!
Here is a simple low register routine that you can do every day. it's a series of drills, scales, arpeggios and long tones in two pages.
It'll take you about 10 minutes to get through it. You should see some improvement after a couple of weeks if you do it daily. You can purchase the routine here for 0.99$