Okay so a few things I feel like I have to say to this

Please make sure you really want to do this because it is a big deal. Making any kind of promise or dedication to a god is serious and needs to be treated as such. And this kind of promise really requires you to believe future you will still be on the same page as present you. I’m not trying to talk you out of it or anything just laying out the reality of the situation. Especially given the nature of Artemis. If she is even a drop of what she is in her mythology then she takes things like this very VERY seriously. 

If you do do this I would advise not using the word “vow” because i think it’s way too similar to the word “oath” and you don’t want to accidentally oath yourself to Artemis. Oathing is extremely serious and something I really advise against for any and all worshipers unless you’ve been worshiping for a very long time and really understand what it is you’re signing up for. So I would use “dedicate” as the word of choice. Even “promise” is better. 

So if you do dedicate your virginity to Artemis, I strongly encourage you to make up your own ritual and prayer. This is extremely personal so it should be of your own creation and in your own words.