It sounds like you have successfully completed your project from a work perspective and you are concerned about sloppy paperwork at the start of your project.
You are at the end of your project now, what have you learned? One thing, is that you should proofread your proposal better. How did this make you feel?
Bad apparently. So what did you do to combat this? It sounds like you learned and fixed the issues that could have caused problems in your project.
I would incorporate this into your final write up. It was part of your experience and that's why you go through challenges in scouts. That's why you are working on proposals for projects instead of playing video games.
You got the opportunity to take on this challenge because of all the years of hard work you have put into Boy Scouts.
If everyone could do it perfectly, there would be no value or meaning to the process.
I would address everything you learned from this process in your final write up, including this small matter. What's important is that you finished, and now you will be prepared the next time you are in a similar situation, and that's the Boy Scout Motto.
Also, you could spend some extra time preparing for your board of review, that would help the most.
Congrats from a fellow Eagle Scout.