I had my poor old cat put to sleep yesterday?

The vet had administered half the dose when my poor beautiful cat pulled his leg away the vet took back hold of his leg and re administered the rest of the dose. I'm so riddled with guilt that in his final moments he was in pain with the injection Surely with half the syringe of the fluid already on him he shouldn't have been able to move what pain must he have felt why oh why did his final moments become so stressful I'm so upset that I let this happen in this way I thought his foal moments would have been peaceful how bad am I to let him suffer like that after 17 years of his friendship and loyalty. God bless my darling sparty I wish I wish I wish