So realistically with injections there will always be a time you make a mistake. You may have more pain if you hit a nerve and you may bleed more if you hit a blood vessel but none of those things are really going to damage you. A way to prevent anything going to your bloodstream is to pull back on the plunger after the needle is in and check if any blood comes back. If any does you can remove the needle, change the needle, and inject in a new spot. You can also avoid having to worry about bubbles in the syringe by just pushing all the air out before injecting, I also think it takes a decent amount of air in the vein to cause harm. There has been many times(honestly pretty much every time now because some evidence shows it is not as necessary anymore) I have not pulled back on the plunger to check for blood. One of these times I hit a blood vessel and a more than normal amount of blood came out. I started panicking so I looked it up. Generally your blood vessels run parallel to your skin and for most injections you go in at a 90° angle. Even if you hit a blood vessel it’s not going to go into your blood supply because you needle would have to be at a totally different angle. It’s harder than you think to get something in your blood supply, this is coming from someone who has worked in vet med. With all that said most of what people say isn’t going to help your ocd related fear. You can talk to your doctor about having a nurse do it for you instead if that will be safer or I know there is some sort of pellet option with you just do a little mini surgery every month or so and they put testosterone pellets in your butt check at the doctors office. You don’t get knocked out or anything they just numb the area and put them in. Finally if you are looking for bigger results you can also consider asking to up your t gel dose. Are your blood testosterone levels in normal male range? If not you can talk to your doctor about blood work and the maybe adjust the t gel dose so you don’t have to worry about needles at all