i scaned the QR code on my whatsapp android

Well, Tito can actually understand what you are trying to do over here you need to be a little clear over this one !! Are you trying to use whatsappweb ???

Okay, are you using any app to scan the QR code or you are just using the whatsapp to scan the QR code ??

Well, that's weird if you are just using the Whatsapp scan then it should be working, anyway let us start things from scratch head over to the Settings>Application Manager>Swipe left to all>Look out for WhatsApp clear the cache stored, once done relaunch the whatsapp app, tap over the menu and choose "WhatsApp Web"

Once done it will look like this

Now open the website web.whatsapp.com over the chrome browser to scan the QR code. See if that helps !!

Also make sure while doing that you device must be connected with an active Wi-Fi/Mobile Data !! And again if that doesn't helps I would suggest you try clearing the cache stored by the chrome browser.

@Tito did you tried clearing the cache and the data stored by the Whatsapp by heading over to the application manager under settings ????

Well, that's weird try switching the Laptop/PC as well as the mobile device off and then again On ! Also be sure that data connectivity is available over PC/Laptop as well as over your Smartphone ! Till then I will try to dig something more ....