If you're Uncollected or higher, and you think you ran the wrong thing today, don't panic.
TL;DR: you probably didn't lose anything you care about. Read on for the details.UC players were supposed to claim Uru from their email and then buy the five Caskets they had enough Uru for: C1-5. This would unlock Tier 6 difficulty in the side quest. Then they were supposed to run T6.
However, two problems arose. First, there was a bug at launch where people who bought the caskets didn't unlock anything. Thus, they only saw T1 and may have used their one and only feather to run it. Second, there was some confusion as the game always shows your highest unlocked difficulty
AND ONE LOWER. The idea is if you unlock T8 but you can't do it because it is too difficult, you can fall back to T7. But some players just ran the first one that displayed on the assumption they had to run them in order.
So some UC players ran T1 today because of a bug (now should be fixed), and some ran T5 today because of a mistake. This means they lost T6 rewards and got T1 or T5 rewards instead. Someone might think they are now screwed. But not really. I don't know if Kabam is going to offer some kind of compensation here, but let's assume worst case and they don't. First of all, here's the rewards in question:

So if you're one of the people who ran T1 instead of T6, you lost the T6 rewards and got the T1 rewards. Eh. Ditto the players that ran T5.
Now, you also lost Uru because T6 gives 10 and T1 gives 8 and T9 gives 9. So you lost one or two Uru. But the event contains a surplus of 10 Uru if you run the event in the most optimal way - running only the highest difficulty available starting at T6. So losing one or two on day one does NOT mean you lost any of the higher rewards. You're still on track to get the maximum number of runs of T10 (seven runs) if you don't make too many other mistakes.
Starting tomorrow, run the highest tier unlocked, which should be T6. If you want the highest possible rewards, continue running the highest tier unlocked until you have enough Uru to buy the next casket, buy that, then move up a level. If you make a mistake don't panic: you've just done one too many runs of that tier, and one fewer runs of the next higher tier. Look at the reward chart (
https://forums.playcontestofchampions.com/en/discussion/251119/somewhere-over-the-bifroest/p1) it is probably not a big deal. Just try not to make that mistake on higher tiers, and especially T10. That's when you start losing things you actually care about.
Note: the way Caskets work is a bit weird. You can buy them in any order, because the game is counting how many you open, not which ones. You can buy them in any random order, but you need to buy five to unlock T6, and you need to buy six to unlock T7, and so forth. If you bought Casket 5 only and are wondering why T6 isn't unlocked, that's why. For simplicity sake, just buy them in order. But if you didn't, again don't panic, just buy all the rest starting from C1 and work upward. It'll work itself out.