I think you may have been fine if you had just washed the soil like you did and did not spray. From what I read the main action and benefit of hydrogen peroxide is to the roots as it adds more oxygen. Spraying as Ray stated is usually used as a pesticide.
It is also possible as others said the mix was to strong.
While I was reading I saw that tomato plants actually produce hydrogen peroxide as a defense mechanism. I had so many tabs open I lost that page
Here is an experiment a high school student did
https://csef.usc.edu/History/2013/Projects/J1717.pdf