Rear axle not seating all the way

I'm in the process of reinstalling both rear axles. The hub isn't meeting with the diff housing the way it was before removal though, and I've been left with a bit of a gap. I feel like this it probably something simple, maybe I don't have something lined up? I dunno but I'm having a derpy moment and hoping someone here might have an idea as to what I'm missing. I haven't tried forcing it on as I didn't have to before and I don't want to ding up any threads.
I did just replace the backing plate and bearings but I really doubt that the bearings or retaining rings are the issue.

 

How big of a gap? Pictures of the gap and the axle removed might help. Do you feel it engaging the splines at least?

It's possible the splines got damaged during the backing plate and bearing replacement, and they need to be filed down. That was the case for this guy: https://www.tundras.com/threads/rear-passenger-axle-will-not-go-into-the-differential-help.125280/

 

It's about 3/16" on one side and almost a whole inch on the other. Both reach deep enough to engage the drive shaft. On visual inspection the splines look clean.

 

If the splines are engaged (ie: you can spin the driveshaft by turning the axle) you might try tapping it in with a deadblow hammer.

 

Thanks for the tip. Your right, the splines are engaged, so maybe it could be small imperfections in the splines. After all its bypassed all the other potential hang ups if it made it that far, right?
Both are pretty hard up but Ill give a hammer and a file a try.