How long have you been injecting Test? It’s pretty common that fur guys who’ve done it over several months or so, the penis & testes can shrink. I think what happens is your system detects very high levels of T & then shuts down your own natural production of it. This can also lead to issues w/ ED, sobthis is smthg I would discourage anyone from messing with. I’m not sure if your genitalia will return to normal after stopping T inj’s, not sure but I think some of these changes could be permanent (non-reversible) if you’ve been doing it for quite awhile...
As for the anal issue, if you've only experimented w/ this a few times, it’s possible it may return to near-normal if you stop doing it. I don’t think the premature ejaculation is related to anal stim, might be more related to your use of Test...
I think the only thing you can do for the anus is to just stop inserting anything there. I think over time, if you continue to insert anything larger than your middle finger, it will probably continue to stretch, but if you give it a rest, at least stop for awhile, it might return to closer to your normal size. As for the T inj’s, I would not think injecting just a couple times would have much affect on your penis size.