It's ok to feel the way you do. And I am glad to help.
Keep in mind, you have coped many times with intense feelings and you have been fine. You do have the coping skills. I'm sure your therapist has been working with you to help you and you and I have been talking about it too. So though you may feel alone and abandoned, you do have the skills in you to help yourself through.
It may have been the sudden cancellation that threw you. As you said, you had things you were prepared to talk to your therapist about. You made the assumption that everything was progressing as usual, which is fine. You had no reason to think otherwise. But when you found out she could not be there, you had to do something with the feelings. You may have been unprepared for the sudden change.
Think about how you would have felt if you knew that you did not have therapy today. What would you have done with your feelings instead? Also, think about what your therapist has talked to you about regarding how to cope. If you can, go over some of the main points of your therapy in your mind. You may also want to consider taping some of your sessions next time so you have the chance to hear her voice and words again if she or you ever have to cancel. Ask her to help you go over some ways you can cope when you are not with her. Then use the recording whenever you experience difficulty coping.
Also, try some of the ideas you and I have gone over. If you do not have someone to talk to, you can write me. You can also try out a support group on line, even if it is just for a night or two. Read something that helps, a book about how you feel or your favorite author. Anything that makes you feel better.
Most of all, keep reassuring yourself that you are ok, because you are. Write it down, repeat it in your mind and/or ask others to tell you. Since you will see your therapist again soon, use this time to write out what you wanted to tell her so next time you can recall everything. It may also help you feel more connected to her and less like you didn't see her today.