Nice! That centerline helps a lot especielly when you get used to doing some contour lines, you can draw the centerline following the contour of the glabella nose lips etc ( like the contour of the digure in profile) and check yourself. Helps a lot with foreshortening like you are doing in 2/3 view
It helps to use plenty of reference as well
There you can see that the face is usually way less symmetrical than you imagine, its more important to get the major structures like the skull shape and the proportions right first, then adding the features which tend to be slightly different from eachother (depending on the figure)
Also, note that the hollow of the philtrum starts just a bit above the mucosal lining of the lips. There is usually a little bevel or bulge above the lips lining
Cheers!