It is true that injections should be slow. As well as the reason of the needle causing less damage, this is another reason to prefer 25 gauge for a 3 mL syringe, as it naturally makes injections slower, though it’s still possible to inject faster than optimal with a 25 gauge. But you have to try, so to speak.)
Slower and better yet is using a 1 mL insulin syringe, 1/2 inch, 29 gauge.
Just imagining the situation, is there magically a 3 mL (or whatever) cavity in the muscle ready to take in the oil? Are there big conduits built in that are ready to take it away? We know that’s not so.
Rather the oil either can only seep between the fibers, which occurs only slowly, or the muscle is getting kind of brutalized and temporarily forced apart at the injection site. Not really the best.
Besides, including 1 mL insulin-needle injections opens up far more sites for injection, and thus build up of scar tissue can be minimized or actually zero.
That isn’t to say it isn’t sometimes convenient to do a 3 mL glute injection because it can be. But as the sole means of delivery, that’s not best, IMO.
It’s also probably not a bad idea to have on hand good antibiotics, which these days are pretty easily available via the Internet, just in case. Infections are rare overall, I’ve never had one, but I’ve almost always had some Cipro, cephalexin, and doxycycline on hand just in case. (Just as one combination that is unlikely to fail. If using only two, it would be the doxycycline that was best dropped. Using “only” the first two is already better than most MD’s do for you.)
However, so far your case does sound more like having injected too fast, fortunately the better alternative. Best wishes on it!
Might be an interesting experiment, I’ve never done it, to take a thick hunk of raw beef, a pot roast or something, try injecting 3 mL of vegetable oil rapidly, and then dissect it to see if there’s visible damage. Could be very illuminating. I’ve never done it, as it’s already clear that local injury is caused by too-rapid injection.