1. don't do that once you loose balance drop that barbell
2. look up ido portals squat mobilisation routine it's on his youtube count
and will do you nothing but good
3. do some overhead squats with an empty barbell and stay in the bottom
wiggle around, try to get deeper
4. those squats were ok, all things considered
5. start with an empty barbell end with 50 kg and do that routine i described in the weightlifting section, takes 5.5 weeks and will kickstart your overhead squat, like nothing else. What you think you can't do that because you'll loose something.
I did start with out with an empty barbell - next of the seven cycles I did - I started with 40 kg and ended with 90 kg for 7 sets of 7...
Thats less than three months... and all other lifts had improved, even the partial deadlift like 20 kg from 220 -> 240 kg, could do weighted situps for sets of five with two 32 kg KBs...