Well, that is exciting, yes! You’re not quite off the pier yet, but if you followed package directions carefully that is good news!
The tests are quite accurate, but not perfect. There is also finite rate of miscarriage that is much higher in the first few weeks. I don’t mean a lot, but estimates are between 10-25% in the very early stages. These would be events that might easily have gone unnoticed in former times when they didn’t have these tests. There are various reasons, but in short there is a lot of dividing going on, the implantation doesn’t always happen correctly, and sometimes the baby didn’t have a chromosomal package consistent with a longer life. When a pregnancy goes right, which it usually does, a LOT has gone right! The hazards of a biological misstep, while less likely than otherwise, are much higher in the first 13 weeks, no matter what the mother does. Still, you are looking at something like an 70-80% likelihood that you do have a viable pregnancy started!
IOW, while you don’t know you’re successfully pregnant quite yet, you do know enough to take extra precautions with your own self care. Your chances are excellent!!! Not a sure thing, but excellent!!!
You can’t ever go wrong with taking very good care of yourself when you may be pregnant! If you weren’t pregnant after all, and just have a delayed period, you will have your health in the best shape for the next ovulation. You will probably do the best if you wait until you are 13 weeks in before you share the news with any but your closest (and most discrete) circle, though. Somewhere around that time, you may have people guessing, anyway, so then you can let your secret out!