Use smaller needles, don't use dull needles, and squeeze around the injection site to ensure you don't hit a muscle.
Scientifically, women need more body fat than men so this sounds like an issue with how you're injecting rather than worrying about your body fat being too low.
As a side note, I actually prefer 5mm needles rather than 4mm because the 4mm are too short. I found myself pressing to hard with 4mm needles (to avoid a lump) which increased the likelihood of hitting a muscle.