A mill doesn't do squared inner corners well, they need to be rounded, like the bits are. The tighter the corner the smaller the bit, this means more tool changes and more cuts and therefore more cost. You got the sides but missed the bottom. You would need a flat end mill to create the sharp inner edge, where a rounded bottom corner (chamfer or bevel) would allow for them to just use the same bit they used for hogging out the main chamber. This also eliminates what are called stress risers, places where stress accumulates, not that strength is really an issue here but it can also cause issues with paint and anodizing. It's inside so again, not really an issue (unless you're selling them), your biggest thing is the added expense of creating it. Doing this on the inside is good for the reasons mentions, doing it on the outside is just the opposite, it can mean another tool change and more cuts.
I didn't look at any dimensions, but don't get super precise. 6in or mm is not the same as 6.0000, 6 means if it's off by .01 it's fine, 6.0000 means that the surface finish needs to be at least that precise, which is like a mirror vs sandpaper. That means more precision, more cuts and more tool swaps. This is why so many cheaper cases are blasted and then anodized, it hides the tool marks from using lower tolerances. If you want a really nice surface finish right out of the mill, you need to pay for it, and this is how. This is also how what could be a $500 case quickly turns into a $700 case.
Also make sure your measurements are whatever is the norm in your country, if you take a metric patters to a US shop, they may send it back and ask you to convert it for them. They should be capable and their machines should be able to do it, but some machinists and their machines are still stuck in the dark ages.
Screws...
Mcmaster-carr has tons of fasteners, and the cad file for them so you can verify sizing or simply import them. Don't just assume you can find something with a smaller head. CAD doesn't work on assumptions and guesstimates, it does everything, EXACT. There is no fudging, there is no good enough or close enough. That's one thing people have trouble with, when you make something yourself if it's close and fits, it's good enough, CAD doesn't really understand that. Close enough and fix it later means you're just going to pay later.
Another thing I'd recommend is a 3d print to verify everything, especially if this is your first.
One misplaced screw hole or bad judgment means you are either breaking out a drill or Dremel or you will be paying twice and considering the cost of making one these vs the cost of getting it 3d printed or even buying a 3d printer and doing it yourself, it's a wise investment. This adds a whole new set of challenges, but can save you a lot of money. This is actually what 3d printing was made for.
Next time you do this:
Use generalizations, okay so I lied about CAD not liking guesstimates, sort of... Take for example your USB breakout board, you don't need to render every resistor and cap, just do a plate for the pcb and another on top that represents where the resitors and caps are and need clearance for, then a third for the rear connector and 4th for the USB port. This is 4 components to render rather than 12 or whatever. Same for the keyboard pcb, you don't need every resistor just something to represent that you have clearance for them.These all still need precise measurement (so, not a lie), but it doesn't have to be visually accurate.
If you do switches, it doesn't need to be accurate in every way, it can be a box for the body, another box for the stem, and then two small boxes for pins and a circle for the stem bump on bottom. You don't need to render every angle and recess. They're only there as placeholders to check clearance.
