There is currently an issue with Real Racing 3 where players cannot complete downloading the game assets. This will appear as though the download progress is "stuck" at a certain percentage and won't proceed any further. Unfortunately this means players may not be able to launch the game, as it will continually try and download the assets from our servers.
Our development team are working hard at fixing this issue, and as soon as we know more we will update this article with new information.
In the meantime we suggest you force close the app, change your connection (from WiFi to cellular data, or vice-versa), then re-launch the game to try and download the missing assets. DO NOT uninstall the game from your device, as this will cause you to have to download the entirety of the assets again.
We are very sorry for the frustration that everyone is currently feeling, and hope that we can have this fixed as soon as we can.