Perception matters. 80% of startups fail, so when you describe your business as a startup, you are instantly associating your business with the perception of instability and uncertainty. If you’ve done your research on your space, have a clear plan on how you are going to obtain your customers, sell your product, reach break-even, and continue building your business, then there is no reason to give people the idea that your business is anything but solid. If you haven’t done your homework on those things, then by all means call yourself a startup.