If it were me, I wouldn't hedge my bets on that last school. If a POI isn't sure they can take a student at this point, then it seems unlikely that they will. Did you have multiple POIs at that last school? If so, waiting a bit more might not hurt, depending on the size and funding situation of that school. If you've already received an official offer from the first school, then you technically have until April 15th to give them a yay or nay. I would wait for next week to send an email updating the first school on your status (that is, assuming they haven't been prompting you for an answer). I think it's fine to take your time; they understand that we are all in this waiting game... Best of luck!