I want to make a shooting game for iPhone n androids. i was wondering if that was possible with this program also i accidentally chose to make the the game on ‘web platform’ will i still be able to make it ?
You have chosen the good one as you can export web games for Android/IPhone (using Intel XDK).
But, you can still change the platform you are using : just make a right-click on the platform’s name in the extensions list window.
1- You can switch the platform: in the extensions window, you can select Web or Native (note that some actions of native platform aren’t available for the web) 
2- You can export GD games to Android/iOS through Intel XDK (you need to download it, I think). And you have to export it to Web first, so you have to use the Web platform 
EDIT: Hahaha, again I didn’t note somebody has already replied 