That advice that you got about relaxing is 100% on. A man can concentrate so much on this game that it'll eat away at you and drive you nuts! you'll end up thinking about thinking, second guessing yourself and others, finding fault with yourself mostly, then soaking in self pity if you're not careful.
One of the strangest guys I ever coached was a guy that dropped out of college in his junior year because of finances. I saw him play for his college ball club and I was so impressed that the following season he was pitching for us.
Now this guy was in and out of the mental game it kind of bothered me for a while. BUT, this was his way of clearing his mind, settling down, breath-exhale-breath-exhale. So I dropped by his room one afternoon just to see how things were going. I entered his room and he wasn't bunking with anyone. He paid for a room all by himself.
Come to find out he was studying to be a entomologist in college. Somehow I never picked that up. In any event, he had trays upon trays - drawers like covered in Plexiglas, full of bugs stuck with pins. Beatles, moths, spiders, and stuff that I never saw before. ( no wonder he was alone)
So look, find something to occupy yourself with that'll take your mind off baseball. Be flexible enough to discipline yourself to do the job when called for, but then let it go. Heck, stick a bug if it makes you feel good. Just be mindful how others might react to your mental gymnastics. (My guy gave me the creeps.)