Hi
I bleed and inject people daily. Don't panic. It sounds as if you may have just nicked a capillary or vein. As a rule of thumb, use the smallest gauge needle you can to inject, and the largest you can too bleed.
For injecting something like T or E which are very fluid, I would use a 26-24 max. I had a flu shot with a 28g, I think a 23g is getting a bit big for i.m. purely my opinion, it hurts too much for me. I take blood from people with a 23g at a push, usually use a 20g. BTW the smaller the number the bigger the bore of the needle. Hence a 16g is used to take a blood transfusion (500ml) and a 20g for a blood sample (10ml).
If you do bleed post injection, take a cotten or gauze swab, place it in the area and apply firm pressure for a few to several minutes. If you develop bruising aleo vera ointment seems to help. If you develop a hematoma; basically a blood blister under the skin, don't panic. Aloe Vera again can help. Don't inject through it as you will bleed and it can be painfull. They tend to look worse than they feel.
You are unlikely to inject into an artery, they tend to be deeper than veins, at least in the limbs. If you do they may spurt! Again apply pressure and sit quietly, if concerned and the bleeding doesn't stop call an ambulance. This would be an incredibly rare event from an injection. However if you are doing a DIY type of project and slip with a power tool you may get, or see someone get into this situation. TIGHT torniquet and medical help ASAP. Loss of a lot of blood is very serious, but a little loss isn't. Generally, if in good health, you should only have an arterial bleed following a trauma. Car crash, shooting, child birth (rarely now I think, but it may be management), or other major accidents. (pun intended)
THESE ARE MY OPINION AND MY OPINION ONLY, THEY ARE NOT TO BE TAKEN IN ANY WAY AS PROFESSIONAL ADVICE. SEE YOUR DOCTOR IF YOU HAVE ANY SIDE EFFECTS FROM ANY PROCEDURE.
Just my opinions
Cindy