There is some information on the ACT site, see http://www.act.org/content/act/en/products-and-services/the-act/help.html ,and open the question “How can I add/change my college choices or correct my high school code?” Read the last couple lines which state that for any state mandated test, changes to your college list cannot be made after you hand your answer folder to the test administrator on the test date. That would indicate you have to make the change by tomorrow morning.
As to whether your high school will put the scores on the transcript sent to colleges depends on high school. Many do but many do not. You should specifically ask the high school what it does and do not just rely on reviewing the usual semester transcript you receive to see if the scores are absent, because the high school may include information on the full transcript sent to colleges that does not appear on the semester transcript.