Maybe try to do it with a harder erection, and forget about jelqing the head repeatedly, just do one strong reverse jelq and then hold the two hands as hard as humanly possible so you feel the shaft is ballooning and gets *very* hard.
What grips are you using? Palms up or down?
I did it palms up for a long time and gained a lot in the first couple of months. Now I started doing them palms down (in both hands) and I feel I can get more intense with this grip. If you do try this though, you have to make sure the first palm down tourniquet hand is grabbing the base in a way that pumps up the rest of the shaft. For this I kegel hard, grab it at the base and then slide it just a little upwards along the shaft, just a tiny bit but it pumps the rest of the shaft so it’s ready for the head reverse jelq which I also do palm down.
If you’ve tried all this before and you don’t feel it makes a difference then do consider pumping, it will increase your girth.