Contact the admissions office of each school and explain your situation. I would even sign up or the next available ACT so that you have scores for schools who might not have space available so late. You would have to pay a late fee to sit for the April ACT, but at least you could send in a complete app before Summer starts.
There’s an act in April. You can use another waiver for that. Hurry and go see your guidance counselor on Monday first thing because the regular deadline has passed but next week there’s still time with the late registration period.
Considering the students ’ reply date is May first, yes may is too late to take the sat, especially if you need financial aid.
What are your other stats - GPA, honors classes?
Where have you applied?
Have you completed FAFSA?
What state do you live in?
What’s your parents’ budget for college?