If you apply ED you should be pretty solid. For ED admissions they seem to focus a lot on ACT scores (they seem to admit a lot of 33-34+ ACTs with lower grades than you) so you should have maybe a 40% chance. Northwestern has a relatively high ED acceptance rate (over 30%), and while a big part of that is D1 athletes, it is still a huge advantage to show that level of commitment to the school, especially at a school like Northwestern that has to compete for yield rates (often unsuccessfully) with Ivies and other top schools.