I certainly don't have all the answers (wish I did) -- but here's my take on it:

The things (or people) we care most about can trigger anxiety -- for those of us who are predisposed toward anxiety. A person (or event or thing) you don't care about will not trigger your anxiety. It just does not matter to you. But things, or events, or people, or relationships that matter to you -- that you care about -- that you feel invested in -- you may be more anxious about. You want them to go well. You worry about losing them. You worry about screwing it up. You worry about whether the other person will lose interest, etc. So the anxiety may be a sign of the strength of your feeling for the other person, of how much you care, of how invested you are.

The best sign is that you can talk openly with the other person about your anxiety. That shows that the relationship has some strength.

At the same time, focus on all the fun stuff, the good times, etc. -- the anxiety is there, something to deal with and try to overcome -- but don't let it overshadow the fun that you have together -- particularly at 17 -- a time of life to enjoy.