They all like you. And they have pillow fights during pajama parties to determine who will get to date you.
To me, it sounds like you just decided to create drama for yourself. You signed Emma's yearbook telling her you liked her. She told all her friends. Then they started asking you if you really did. This could mean two things - Emma likes you and is using her spy network to find out for sure if you like her or she is very surprised and she and her friends are sort of laughing about it. The only way to find out for sure is to ask her out. Take a real chance, not just writing something in a yearbook.
As for Stephanie, ask her out. Again, that is the only way you will know if she wants to go out with you.
If you are still signing yearbooks, there is no need to choose one over the other. You are young and can date whomever you want. No need to commit.
Reign in your shyness, be confident, and go for broke. The worst they can do is say no. And when you think about it, that isn't really the worst thing. At least you will have gained practice in asking people out.
Good luck.