You do not have all the requirements, a mac from 2011 cannot upgrade to macOS Mojave.
Only iMacs from 2012 and newer can upgrade to Mojave.
Open Safari and click here,
https://support.apple.com/kb/SP777?locale=en_GB
This is what you will see,
Mac Hardware Requirements
For details about your Mac model, click the Apple icon at the top left of your screen and choose About This Mac. These Mac models are compatible with macOS Mojave:
- MacBook (Early 2015 or newer)
- MacBook Air (Mid 2012 or newer)
- MacBook Pro (Mid 2012 or newer)
- Mac mini (Late 2012 or newer)
- iMac (Late 2012 or newer)
- iMac Pro (2017)
- Mac Pro (Late 2013; Mid 2010 and Mid 2012 models with recommended Metal-capable graphics cards)