Did you inject after aspirating while observing blood in the syringe? Yes, you would know fairly quickly if you injected into a vein. Blood moves quickly and takes no time to go to essential organs.......like the heart and brain!!!!! I would suggest taking out the syringe if you see blood on aspiration and injecting at a different site. The tricep or any muscle group has plenty of alternate spots. Don't just take the needle out a little or push it in farther assuming that it will not enter the bloodstream.....bad juju