I've just recently started testosterone therapy, and today was the first time I gave myself my injection. Everything seemingly went well, but I noticed roughly 0.025mL of oil left in the syringe afterwards. I'm sure I pushed the plunger all the way down, especially since I tried getting it out after and I couldn't push it down any further. Is this supposed to happen? I'm not too worried right now because it's not much, but if I can't fix the issue I'm worried that it'll accumulate over time and I won't get results as fast as expected.

Has this happened to anyone before? Is it normal? If not, is there any way to fix it?

I take estrogen shots and have noticed the same thing. Some of it remains in the needle and the end of the syringe, but I've also noticed that when I get my prescriptions that they do give a little extra than what you'll use in the bottle by the time for your next refill. As long as you are at the correct mark on the syringe (after) you have squeezed all of the air bubbles out you should be fine. I do this while it's still inserted into the bottle so I can see the air bubbles coming out.