I Keep Things Bottled Up Inside Of Me

So I recently started seeing someone. We both work at the same place and everyone kept wanting us to get together. So one day I just said you know what why not give it a try. Everyone is really happy for us and I'm happy too but I just don't feel like she's the one. Unfortunately I feel like she is moving a little too quick and that if I tell her that we need to slow down that it would devastate her. I also don't want this to happen because I would at least still like to be friends but I don't want ruin that as well.