I agree with @“so_excited!:)” . A number of applicants will also be submitting work from their junior years. Since the OP says his work is a reflection of his writing in junior year, it would be okay. The AO’s would notice that. It can only be positive for you that you also got a good mark. (Similarly, it is hard to speculate how another applicant’s writing level is now, although he/she may submit something from a year or two ago.)
As @“so_excited!:)” pointed out, your current writing level would show through your application essays now. College admissions often focus on the “trend” and “trajectory” of a student’s work and achievements.
If you do not submit anything (and give no explanation), it will only give the impression either you don’t have anything to submit, you have overlooked it, or you have something to hide. Princeton (regional AO’s) have got a lot of data points and will not draw conclusions about your school from a single data point. That should not be your concern now.
If you are really worried about it, I have two suggestions.
(1) attach a cover note to your written submission with a very brief note explaining it–although I think that is unnecessary, and (2) don’t put all your eggs in one basket–make sure you also submit applications to other schools with no written work or SAT/ACT essay requirements.
Fully understand your concern here. But I think you have a reasonable solution in this case, since at least your teacher liked your paper. The high mark will indicate your work was above his/her expectations. I have been to an info sessions at Princeton where the AO emphasized that she wanted to see if you are doing well and taking up the challenges available at your school. (Some schools have more resources and some have less. That will be fine.)
Think about if. If you were an AO, would you prefer someone who has (1) submitted a (not so great) paper scoring 95%, or
(2) not submitted the required written/graded work?
(If you submit nothing, your HS work quality can only be speculated, the possibilities are unlimited. IMHO, it is better to show what you have, than nothing.)
Again, I concur with @“so_excited!:)” , this is really just one of many parts of your application, especially since you are applying to major in STEM. (I mean, if you applying to do physics at Princeton but you cannot do basic algebra, that would be a concern. But you are not.)
Be comfortable with what you have and have not, and move on with your other applications. Time is running out. Good luck!
My Best Wishes to You and All Your Applications!
Just know you have all our support here.