Its for an entire country so I would expect its the largest size ever. Success is really measured over the long term but maybe the launch was really the main concern here.
Telegram seems to be in proportion to facebook, is it really that big.

How were you able to install the Petro wallet?

Go here http://www.elpetro.gob.ve/ and scroll down down down... you will find the wallet to download for Windows, Mac and Linux. iOS and Android are not available yet.

Not sure why but I keep receiving this message when I try to run the PetroWallet file "This app can't run on your PC". I currently have Windows 10 installed on my PC.

Try using a different browser to download the file, might help. In some cases crypto related executables run into problems with anti malware measures. Also right click on the file and select run as admin, its possible you lack the permissions to continue otherwise. Windows 10 comes in a variety of versions, if you can narrow down which type that would help. I did try one version of windows which blocks anything not available through the windows store which is quite an extreme security measure I guess.