What should you do if you shot crack and missed your vein?

If you're attempting to treat yourself at home (not recommended), simply run the injured area under warm water & gently press against it to reduce the chance of an abscess forming. If the area swells or bubbles largely, see a doctor immediately; otherwise, use a warm compress, cleanse it with alcohol, & then leave it alone.

It's important to watch the area for a few days; if an infection develops (redness, swelling, blisters, numbness, pain, etc.) see a doctor as soon as possible for an antibiotic treatment. As scary as it will be, tell nurses & doctors the truth for the reason that they cannot treat you properly if you do not tell them exactly what happened & what you injected.