I disagree with this, with an exception below. If you intend to pursue a graduate degree, it is very bad form to commit to a program and then change your mind afterwards. You will burn bridges at NEU by doing this. Forfeiting the $100 deposit doesn't make up for it.
Instead, what you should do is contact USC and NYU Tandon now. Find out if they plan on admitting students after April 15. What @Ignis said may be true---all these programs might have already finished making decisions and have not yet rejected people, so then you can safely accept NEU's offer.
However, if they tell you that they do plan to make offers after April 15, which is normal because almost every school will give initial candidates until April 15 to decide so it's only after April 15 that they can fill vacancies, then you should talk to NEU and ask for an extension so that you can hear back from the other two schools.
Now, only if you know there is a chance you can be admitted after April 15 from the other schools and NEU refuses to give you an extension, then DealBreakerC's advice makes sense. At this point, although backing out of your commitment will still hurt you, there isn't really an alternate choice. I just would not advise accepting an offer with the intention of reneging it until you've tried all these other options first.
