Why not go to the school you’ve been accepted to attend and take the act while there. You need college class grade verification for the other school as well.
Go. You may love it. If you do well and improve your act then move to your top school choice in the fall.
You already missed time. Probably won’t have a full transfer of credits. Don’t miss another semester hoping to get into school b. Sounds like a bad idea.
Go to school in spring. See how it goes for you and produce the credentials for top school a and transfer in Fall with more credits. If it falls through or act doesn’t pop higher you’re in a great school already.