If you feel presumptuous saying you are the CTO, then you should consider a different position for your resume. A C-Suite job usually means more high-level 'business/administrative' work than hands-on interaction with the field they manage. A CTO will spend more time managing resources, projects, and career paths at a bigger company. If this isn't what you have been doing or what you want to be doing in the future, ask your batchmates if you can have a title that more accurately describes your work and desires.
You could say that you are the principal engineer. It's just about as true, shows you took a leadership role in the technology sector for a small team, but will be looking for more of an engineer/senior engineer level for your next line of business.
At this point you could go two different routes with your career path: you can say that while you were excited to pursue the unique opportunity to be on the ground floor of your own business, you now have an appreciation for many different aspects and skills of the business world and would like to focus on growing your own skill set ( backend infrastructure) with a bigger company.
Or you can say that after the initial funding round and product launch, your team discovered that the market just wasn't right, and now you'd like to move on to a new project, and your unique experience, self-motivation and leadership skills would be great for another young company.
If you haven't completely lost faith in your batchmates, you could take freelance work until the next great idea comes along. Sometimes young firms have to try a few ideas before they bring a viable product to market.
Congrats on giving a start-up your best shot: lots of people dream of starting their own company but never have the courage or chance to do so. When you're interviewing and writing your cover letters, don't dwell too much on the failure of the company. Lots of companies fail quickly, often for reasons that are out of the owner's control. I'll bet you've learned some interesting lessons in this past year that will make you a phenomenal job candidate.