@Angelique-Innocence Since there are not a lot of one piece fanfictions in wattpad, you can read a lot of them on quotev or archive or fanfiction net.
A story in particular, found in archive called Finding Home by polarsky was so damn good! It's like your story about Sakura in One Piece but she got transported in the One Piece world during the The Fourth Great Shinobi War against Kaguya and got De-aged about the same age as Kid Luffy, met Luffy, became friends with him, met Shanks and I really can't spoil more... Unfortunately, it seems that the story got abandoned with only six chapters. The chapters are pretty long though. You should try to read it! And if you already read it...Then I don't really know what else to read. There are really few good one piece stories these days.