You can technically redo Lesson 1 (or any lesson you've already completed) and receive another critique on it, as long as the work is complete. That said, when you get a lesson marked as complete, it's because the TA feels that you're demonstrating enough understanding to continue making use of the exercises yourself - so seeking additional critique of the same work wouldn't really be all that beneficial. I can understand it coming from a position of self-doubt, but that's entirely independent of your actual skill or understanding, and it's best not to fuel that self-doubt by listening to it, as that'll only make it a louder voice in your ear.

As to your other question, as discussed in Lesson 0, students seeking official feedback are not permitted to move onto the next assignment prior to having the previous one marked as complete - so you technically should not have moved forwards. You're in luck however - we do ultimately make an exception for the 250 box challenge. Rather than having students redo it in full, we only ask them to complete an additional 50 boxes after receiving completion on Lesson 1, so that we can see an example of your work here it is currently, factoring in any feedback you'll have received and any improvement you may have had in the meantime. These additional 50 boxes should be submitted alongside your original 250.

That said, you are still subject to the 2 week cooldown, and will not be able to submit your 250 box challenge until the cooldown has elapsed.