From what I understand, you can use pretty much use any object to make a pendulum. Everyone has different experiences with it. Myself, I used a thin string and a diamond earing once. It was fascinating, however, the practice is not a personal preference of mine. I felt as if I invited random 'visitors' in and my gut/intuition wasn't comfortable with it. It's not a practice I care for.
Interesting though about a chart you used, I never heard of a pendulum chart. Sounds almost like how an ouija board works?
However, Id relax, and not give those negative thoughts you had with the pendulum attention. Let that day and event pass, it is behind you now, no need to give what you did power with your thoughts, and at the end of the day, that will be your greatest enemy; negative thinking. If there are protection techniques ( sageing) or blessing your space, I feel that is enough imho... I always sage my room at least once a week, I do practice the tarot. Clear out any energies or curious visitors who like to watch me play, heh