Leave the pin in for like 30 mins after injection the with gauze or whatever apply light pressure for about 15 (don't massage). Can't waste that oil mannnn

I've used the technique illustrated in the link below. Depending on the muscle you choose it can be tricky to execute, but if used it will prevent the back leakage issue your having.

http://www.mombaby.org/PDF/17P%20Intramuscular%20Injections%20Z%20Track.pdf

Ehh, stop warming up the gear. I see your running EO based gear. EO allows for a faster injection due to its viscosty. Defenitily inject slower into a larger muscle group. Even than some people dont care for EO as a main in their gear

Happens to me sometimes as well, doesn't really make much of a difference though. Try injecting into bigger muscle groups such as quads/glutes, in those areas I never get back-flow.

Sometimes I pull the needle out slightly and leave it there for 30 seconds, this also helps...

Inject it a lot slower, once the barrel is empty i hold for about ten seconds until the pressure inside the muscle lowers because if you inject it to fast, pressure will build faster as there is a build up of oil in a small area.
muscle tissue is elestic so it makes since for it to push oil back out. inject slower and the oil will disperse slightly so there isnt such high pressure.
remove it slowly strait out because if you pull the needle out at a slit angle the point of the needle is so sharp it will slice the epidermis(skin) making it easier for oil to leak out and apply pressure as soon as the needle is removed with an anti sep wipe.

I'm no expert but hope this helps.

ive read that sometimes that happens if you have too much air in the syringe when you pin, but it happens brah

maybe you should try using your trumpet instead of flute? lol.
'this happens to me sometimes, especially shoulders its all good bro.

It happens bro, don't worry to much about it.