Hi there...
What a beautiful platy you have there! How long have you had her? When did you start to notice her getting big? They are usually pregnant for 27-29 days and she doesn't quite look big enough to pop yet. They can also give birth over the course of a few days and sadly, I've had one die in childbirth.
I have lots of platies and have had a bunch of births and currently have 23 platy fry in a grow-out tank! Do you have a separate tank to put the fry in once they are born?
Feel free to ask questions and I will do my best to advise...plus there are many other members that know a bunch about platies!