It's best if the title you present to the world reflects what you actually DO. If it's just you, "Owner" is best. If you have two employees -- say, a book keeper and a web designer -- figure out what you "do" and that is your title. If you're an engineer, "Owner and Engineer" might be the way to go.
You're not going to fool anyone with just the title "CEO". They are going to ask you pointy-headed questions and you're going to get nowhere with that. In particular, if you claim to be the "CEO", you might get asked business executive questions you just can't answer. You'd have been better off with "Engineer" in your title -- at least you could answer those questions.
You can call yourself whatever you like.
Personally, and this may just be because I'm British, I find anybody labelling themselves CEO in a company with less a three digit employee count just a tad silly :-)
In Silicon Valley, it's common for early-stage startups to use the title CEO if it's a high-growth company and their job includes things like pitching investors and building partnerships.
But what's common in Silicon Valley might be viewed differently in regions with different culture.