I did a little google search and found that a lot of people have had trouble with that same chest. I'm guessing that there simply isn't a star key in that tomb, or at least there's 1 short, so when most people get to that point they can't open the box unless they have a skeleton key. I didn't have one with me on that adventure, but I certainly did buy one afterwords! And check it out, I've already used it for something so now I need to get another one. Never thought those would come in handy, but apparently they do!
With my sim Aria, I had that problem. Found no star key, even used testingcheats to enter build mode and look for any hidden room or treasure I might have missed; but nada. She didn't manage to complete all adventures before a bug made her family unplayable, unfortunately. Real shame, I made her house so nice, too.
With my sim Arianna, on the other hand, she had a star key in her inventory from some other adventure when entering Dong Huo's treasure trove and opening the chest. I think there must be some adventures where you find keys that don't fit into any panel in the particular tombs of the adventure, but instead can be used in other adventures. Arianna has (I believe) finished all adventures, and opened all key panels, and I can't remember if she may have had a key left in her inventory? But I don't think she does. She's never used the skeleton key, never even bought it. So I think the number of key stones and key panels should match.
Just go out and do more adventures, and then when you're done, go back to those chests you couldn't open before. If the number still isn't even, you can just use the skeleton key or cheat.