Trimix failed attempt

Hi all

i am 40 years old fit guy with psychological ED due to lack of penetration experience.

pills work for me and i do get erections but it goes soft when i penetrate.

got trimix and worked perfectly for the first 9 injections. i was taking 10 units and injected 9 times over 2 months with great success.

however yesterday after a 2 week break i tried injecting again and got hard immediately after some stimulation from my gf

but as soon as penetrated it went soft after a minute. normally after injecting trimix i get an erection in 5 minutes and then it fluctuates for the next 20 minutes and finally it becomes rock hard and stays hard for 2.5 hours

however yesterday it was a disaster when it didnt stay hard and went soft. stayed chubby though

what could be the reason? is this injection technique gone wrong? is it the dose or is it the vial?

please advise