You can feel "contradictory" feelings. That means you feel two opposite feelings at the same time. For example you can feel happy and sad at the same time. If your part of you tells you that, objectively, you have a good chance of success, but at the same time you feel that you are certain to fail, then you "have contradictory feelings."
"Complicated" feelings means exactly that, feelings that can't be described simply. For example, most people have complicated feelings about their parents. It's not as simple as "love and hate at the same time," because the feelings might also include respect, admiration, contempt, anger, and friendship.
If you _only_ feel that you will not succeed, then you are not feeling contradictory or complicated feelings. I can't think of a good single-word adjective. I would just say "I have an irrational fear of failure." "I feel certain that I will fail."
You can "feel conflicted." That means that you are trying to decide something, and you can't, because you see problems with every course of action. When you "feel conflicted" you are stuck. You can't make a decision. For example, suppose you see an announcement of an audition and you are trying to decide whether to go. You think "I should go, I can't get the position if I don't audition." And then as soon as you half-decide to go, you think "No, I shouldn't go, it will just be more disappointment and heartache." And then as soon as you say "I won't go," you think "Oh, don't be silly. You have a chance. Go for it." That is "feeling conflicted."