If your computer froze, you should be able to get a free retake. I would contact GMAC about that.
Education and GPA are top notch, especially with an engineering major. 3.6 is very impressive for that major.
Have you been or will you be promoted before you leave the software company? I would suggest having some sort of promotion before you leave that company.
All that said, your education box has been checked and gold starred. What is left will be your work experience and extracurricular activities. I would suggest getting involved with something in your community that you are passionate about. Something that has an impact outside of just yourself. For example, I am passionate about helping under-resourced communities, so I am involved almost every week with multiple non-profits that tutor and mentor in those types of communities. I know others who are involved in such organizations as Habitat for Humanity and Big Brothers and Big Sisters. All of these types of activities help others and have an impact outside of just yourself. Pick something you are passionate about and get involved with it.
Your work experience is what will be higher risk. When you work for a startup, admissions committees have a harder time judging that work experience. Not that working for a startup is bad, but it is harder to judge. When you are promoted at a more well known company, admissions committees can have more confidence in your abilities because they know how tough it is. That's why I would suggest having some sort of promotion before you leave. Make sure you also have documented your accomplishments at that company.
You said that you have already received several hundreds of thousands in funding, so it sounds like you are off to a great start. If you stay with this startup, I would suggest routinely documenting accomplishments that are numbers based - $400,000 in funding, 500 students registered with an average 20% increased test score, operations in 15 countries, 200% revenue growth in 3 years, etc. Numbers usually have a bigger impression.
You are off to a great start, and it is awesome that you are getting started so early. Good luck with everything.