Even though your platy is pregnant, you probably will not get any fry from it. If platy's are stressed they will abort their pregnancies and you wouldn't even know. In order for livebearers to give birth they need to have perfect water conditions. They will mate in less than perfect conditions but the chances of them giving birth in them is slim at best. Your tank needs to be cycled and has to have the right PH. Just so you know, platy's as well as other fish will eat the fry. So you will need to get some breeding equipment or a nursery tank ( that also needs to be cycled) if you plan on sucessfully breeding platy's or other livebearers.
Cheers