My last PIOs, the first two nearly killed me. They were a more highly concentrated form (100 per something), requiring half the amount to be injected -- 1cc. When I changed to the lower concentration of 50 per whatever, and 2ccs to inject, all was fine again. Maybe you could check that.
Otherwise, there is a pretty wide range of where you can shoot - if you are in the wrong spot, you will FEEL it right away. It will hurt. That's the main concern, not whether you are getting it into your bloodstream.