Oh ouch that looks pretty bad.
Did you use a clean fit? Did you wash the area?
Is this a new batch of drugs or have you shot this same batch before?
Did the whole shot empty into the vein?
It could be a very leaky vessel leaking under your skin mate.
You could have touched on a nerve close to the skin or shot into a vein valve so it could just be a leak which clears up in a couple of days.
Suggest keep a close eye on it, put a compression bandage on it to encourage healing. If you do not have one the a sterile plaster on then cut the top of a clean sock and put over.
If it is hot or dies not get any better over the next day, sorry, it's off to the doctors for antibiotics.
Doesn't look like an iv incident that much and could be any wound so it's sane antibiotics for wounds no matter how they happen.
There are wound plasters and poultices at chemists.
Hope you feel better soon.