Most of the time being confident and being terrified are emotions with a negative connotation. But, when you have them at the same time, this might be interesting.
I have these feelings often at the same time. Mostly in times when I have to come up with creative ideas and solutions.
Confidence as a starting point makes that I actually start with stuff, ideas, possible solutions, and it makes that I start with something. Start calling somebody, ask for help, build a website, design a project, e-mail someone with a difficult message or question. Together with the terror of not knowing, feeling insecure, or ashamed, makes it that there is always an edginess to the action or the possible solution I bring up.
These two emotions at the same time also allow me to not know. And, when one does not know, one starts asking fundamental questions. " is this something I really want to do", " Is this something really necessary".
It can really be scary, because people might think you are stupid. Because of the strange questions you ask. Or the strange solutions you come up with.
Always when in a state of terror and confidence, start doing, start asking. It helps you to design the right actions and answers.