28 ACT too low for Brown University?

Assuming all my essays are on point and I have done a good amount of focused extracurriculars, do I have a chance?

Unlikely. Per the Common Data Set, 13% of enrolled students had an ACT of 29 or below. But my guess that a good chunk of them are recruited athletes or similarly hooked.
https://www.brown.edu/about/administration/institutional-research/sites/brown.edu.about.administration.institutional-research/files/uploads/CDS_2017-2018.pdf

You’ve asked this question before and received similar responses:
http://talk.qa.collegeconfidential.com/brown-university/2073300-i-want-to-go-to-brown-university-but-i-have-a-low-act-sat-scores.html#latest

Yes. I’m a first year at Brown and a non-athlete and my SAT was equivalent to a 28 ACT and I got in. Not saying you have a great chance but it’s not completely hopeless.

Depending on your ECs. If you have a 'hook;, then you still have a good chance