You may find the following information useful:
#1. 23gauge 1.25inch isn't necessary for glutes if you're 15% bf. You are only creating tons of scar tissue for no reason (unless you're only hitting your glute once every two weeks or so)
#2. I suggest trying 25gauge 5/8, but just make sure you are keeping your skin completely flat when you press it in and make sure it stays in without moving.
#3. The reason it's easy to go in sometimes, and sometimes it's hard is because you are putting it in an area with scar tissue. You need to use some different sites, OR use different sites on your glute. You can actually get about 3 different areas on your glute(top of your glute,lateral....top of your glute,more towards the middle......middle of your glute but don't go above 5/8 inch so you don't hit the sciatic). I do NOT SUGGEST YOU DO THIS, but it is very doable and I know people that do it with no problems whatsoever. I highly suggest you rotate Lglute->Rglute->Ldelt->Rdelt->Lvastus->Rvastus->add other sites if necessary so you only hit a site once every 2 weeks at the very minimum
#4. Start rotating sites because you have clearly already built too much scar tissue...that's why it won't go in easily
#5. It makes no difference if you inject SubQ versus IM except it won't reach your bloodstream until literally less than a few hours later(it could even just take an extra 30-60mins max btw). The reason we do not give SQ injections of testosterone or other anabolics is because
A) It is rare to see an individual taking a very small quantity(in ml/cc) of testosterone or other anabolics, and you can not handle too much oil via SQ. I wouldn't even go past 0.3-0.5cc IMO,although I know people that have done 1cc SQ no problems...but I just really don't think it's a good idea because:
B) It increases your chance of infection and abcess, so you really don't want to deal with that
#6. Since it does not matter if your testosterone has been going SQ or IM - there is no reason for you to worry about it having been 'wasted'. But make sure, from now on, that it DOES go IM. With a needle that big at your bodyfat, I'm essentially positive it is going IM.
Good luck and stay safe.