What Causes Stiffness In The Neck After A Heroin IV Injection?

I just missed about .1 cc of heroin into my side neck vein. I am an IV drug user. I never have missed in my neck before and I knew I was not in the vein because I felt a sharp pain from the site of insertion down my body. After I pulled the needle out, my neck has got very tight, red, swollen, and a white welt has swollen up from my neck around my shoulder, all the way to my back. My face is swollen and flushed. I put ice on the welt but no change. I am typing this question for some insight. It is obviously not so bad that I need the ER because then I would not be online, I would be in the hospital or clinic. It is just kind of concerning. Any help or input would be appreciated. Thanks for your help and knowledge.