Impressive for 10 mins :)
Because I believe you spent a while on the face that caused it to be darker, I would recommend picking out the shadows of the whole object before you focus on the details of a specific part (like the face or hands).
You could lightly mark the facial features if that is what you feel like doing but reframe from getting them that dark until you are pretty comfortable they are correct.
I'd check out the video '1-Minute vs 5-Minute Figure Drawing: Quick & Dynamic Sketching' by Marco Bucci, he gives a nice demonstration, including shading, then have a go at doing that again a few times with different photos :)
It will improve your use of light and dark values and change how you spend your time when doing these timed sketches :) Wishing you all the best with your drawing!
