Using one hand for jelquing and the other to squeeze at the base is probably good, will trap more blood. Also I believe doing it close to erect is better (but don’t do it rock hard - you may hurt yourself and it won’t do much anyway IMO). Lately I have been trying to concentrate the force on the sides of the penis since that is where the chambers are and most of the nerves run on the top of the penis so it may not be good to apply huge forces there.
I think the main thing is to be aware of how your penis feels while/after exercises and tweak your routine to improve it. For me small changes made a big difference. For yourself, those changes may be different than my technique.
As far as stretched, it seems like my rock hard erect length is slightly longer than my stretched length but this may be due to the fact that the skin at the base gets pulled out when stretching it so the measuring device cannot be placed as close to the body. I wouldn’t get hung up on it.
Also, I don’t believe you can really say something is or is not working (except for the “feel” as I said above) until after 2 months so resolve yourself to stick with it for 2 months.
Good Luck