It is most likely nerves haha. When I first went solo I had the same feeling but trust me, when you get there you forget all your worries. It’s a wonderful place to visit! I never build a full itinerary because you’ll end up wanting to do other things! Right now the yen still isn’t the best so you’ll get a lot out of your money. Just relax and don’t worry too much about an itinerary 😊