you look like you may be yes.... but MAYBE NOT...TOTALLY hard to say

you didnt mention at least as far as I could see how long you have been lifting for in total.

I would say that from the looks of it you are doing 9 total working sets for shoulders at a range of 6 to 8 strict form.

if thats the case..then I wouldnt say that you are undertraing.. BUT, it(fat) could be building up simply because your body is ready for more....

I train instinctively, I have for over 13 years naturally ... with that said I have a pretty good inner voice shall we say as to when I can or should not do one more set... I listen to it.

I do however go to extreme pain failure sets never over 20 reps and always use a different range of reps....

I used to have a notepad and write down what I did and the reps right down to half reps and rate how I felt the next day and comment on the workout in the book the next day thereafter to see what I was responding to and not to...

I suggest you get a book, blast yourself...see what you respond to.. try new things...test yourself.

use some higher reps, mass is not built solely on reps, imo its built on stimulation...and sometimes muscle can be better stimulated at a higher rep range before nervous or tendon exhaustion.

good luck fella