This took me longer than it should have
. Alright... so, I just don't see what could be wrong there, this looks right. Try putting the inject file into the root, and if that does not work / if it was already there, put it into /Decrypt9/. If you already have a9lh, you can try injecting with Hourglass9 - that will also do it.
And, if the problems persist, it might be an issue with your SD. That could especially be the case if you formatted with Easeus Partition Tools earlier. The recommended means of formatting 3DS SD cards is EmuNAND9.