twigdip,
If you look in the last picture of your first post, the problem is not the nut, its the fretboard.
Personally, trash that instrument, and get a new one. Its issues like this that will cost more to PROPERLY repair, than the instrument is worth. But, since you asked. . .
If the intonation is correct, then you should replace the fretboard, cut with a proper angle at the end of course.
If your intonation is off, and gets correct when you push the nut up, then you should replace the fretboard. OR, you can replace the nut, cut with angles to match the neck and the end of the fretboard.
There are a number of guys that will tell you to shim, both nuts and saddles. Personally, shimming is the first part of the fix - its only to find out where you need to go, then you go and do the whole thing over from the beginning (meaning, shaping the nut from scratch).
BTW, your slots need to be addressed as well.
Caveat - I am talking about doing things that an upper end would have done (or shouldn't have to). In the end, its a cheap instrument, leave it, play it, and be happy (and see the Uke Minutes video on buying an instrument).
-Aaron