The board said that the second oldest boy would marry a girl by the name of L. which came true, even though, at that time, he didn't know anyone with that name.
Power of suggestion? Self-fulfilling prophecy? In his subconscious, he always carried that name in his memory since that incident and when he met a woman with that name he asked her to marry him. Belief is a powerful predictor of behaviour.
Tec: You were alone in the second incident, but you still had your hand on the planchette. Did you watch the video posted on the ideomotor effect? It is a well proven and well documented behavioural phenomenon.
The first incident I have no explanation for, but it wasn't a very compelling witness. You admit your memory is sketchy. You admit you had a very active imagination and worked up the fear (and expectation?) within yourself. Please don't take that as a criticism of your story or you. I intend it only as a more plausible liklihood.
I had an active imagination as a child too. I could have swore the eyes in this creepy painting were moving and following me every time I babysat at this one house. Now, I'm 100% sure I imagined the entire thing. I imagined demons around every corner as a child. I was terrified of ouija boards too, because I was conditioned to be terrified of them. Now, I would have no problem having a piece of painted wood in my house. If demons really wanted to contact me, they could just talk to me outright. Why would they need to spell things out on a painted wooden board?