The discontinue rule is 3 in a row incorrect, yes. I can't speak to whether your perception that the previous answers were correct is accurate, since I don't have your actual responses, but I can note that some items on some subtests can have partial credit, in which case a correct answer may not receive full credit, if it was missing some element, or slightly too vague. (Having confidence that you were correct, obviously, is not the same thing as actually being correct.) Most likely, she did count the ones where you self-corrected, unless you did it a few items later, after you had seen subsequent items.
I also should mention that, generally speaking, your visual-spatial skills are relatively weaker than the other areas (though still comfortably average). (This is usually considered a kind of nonverbal learning difference or disability.) It is possible that some of the answers that you feel were correct on matrix reasoning were actually reversals, rotations, or inversions of the correct answer. In that case, I could see how you would perceive them as correct, (and on some level, they would have correct reasoning elements to them) but they would be marked incorrect.
All this being said, I would encourage you to be comfortable with the fact that you are an intelligent and capable individual, and address the anxiety and self-confidence first. We all have strengths and weaknesses in our learning profiles (and our overall human profiles!); this is not a mark of failure or deficiency, but of natural variation, and the complementarity of living in community with other humans. You appear to be good with language and with abstract thinking, and less strong with spatial-perceptual skills and (as a corollary) motor speed. That's okay. It probably means you benefit from giving yourself plenty of time to adjust to a new situation, and to learn the nonverbal communications of new people, and that leaving breathing room before and after tasks will help to take some of the stress out of them. Clarifying what the expectations are before you enter a new situation or begin a task will probably help you to reduce anxiety that emerges from uncertainty. Start early, pace yourself, and take advantage of opportunities to check in occasionally at reference points--say, with professors--to confirm that you are meeting expectations. And when they've approved a component, leave it alone, and move on to the next part.
