If I can’t do it I can’t do it. I don’t feel bad about turning people away, even friends and family. You cant overbook yourself by taking on more then you can handle and if you already have other commitments that isn’t your fault! People have to understand that you have a life on top of your work/hobby and that sometimes you wont be available. Those who want better chances of having you available have to learn to order months in advance! That’s just how it works, don’t be hard on yourself!