A little bit too soon. On the other hand, there is no such thing as "when should you do this and when is the time to do that?", Every couple is different. If you guys click and you are sure she feels the same way about you, then go ahead.
But maybe follow the advice others already gave you and try & kiss her first. If you haven't already.
How do you make it official? Usually it comes natural. When you spend a lot of time together you just start calling each other bf/gf. The simplest way is probably though, just telling her "Hey I like you, can I call you my girlfriend?" or something like that.
"If you love life, life will love you back."
Arthur Rubinstein