Advice on how to play on an off day?

I practiced a lot this week in preparation for a tourney this weekend. I was noticing I was playing good and felt good going into the tournament. I sat down watched some people play friendlies. I joined in an immediately noticed I was off. I was flubbing a lot and missing things I normally hit. I just overall was not as sharp as I was previously. The tournament started and I did super poorly. I lost to people who I felt like I could have beaten. Any advice on how to play better when you know you’re not on your A game?