Seeing that you have been off (low dose T replacement) for almost 8 months as you are trying to recover your natural (endogenous) testosterone levels than it would be a huge mistake to even try a 100mg shot of T just to try and experience a boost in your libido/mood.
Even though you just had blood work done and need to wait 7 days for the results just stick it out.
One shot of 100mg would not shut ones hpta down as it would take anywhere from 2-6 weeks of being on exogenous T for that to happen.
Just wait for the results and decide your next move from there.
I know it may be tempting to just do that one shot and seeing as you already had blood work done there is no way the results would be skewed if you decided to take the shot but really.....why bother!
Even if you did experience a boost in your libido/mood it will be short lived and temporary as that is expected when one first starts on exogenous T.
Say you took the 1 shot and experienced a boost in your libido/mood and than next week you find out your TT/FT levels are descent and you are going to continue staying natural.....than that 1 shot may tempt you into thinking trt will end up being the better choice.
Just wait it out as you have already been off trt for almost 8 months.....what is an extra week!