Re-download my app from google play dashboard?

So it is a possible to download the apk that you uploaded to the play store, to a device and retrieve the apk off the device. It will be the same apk your uploaded. There are also tools to download it directly to the computer though they are a bit sketchy. There is not option at this time to download the apk. But you have to remember that what is on the playstore is a compiled apk and not the project files. If you just want the apk to upload to other devices that will work fine. But to further work on the project and change the code will be some work.

From there you would have to decompile/reverse engine the apk, You will have to use a few apps so you can retrieve the code. It will not be the same (though I have heard apk's decompile fairly clean) but it will save you a lot of work from starting fresh. Look up decompile/reverse enginering an apk on google.

Now this a lot of work, If the app is a life work projects It would be worth it but if It is just a project your are playing with I would not recommend it.

As always backup is the best option. LIke Harry James said, git is an awesome way to keep your projects organized and have different versions of your code backed up. Also utilize a box service like google drive or a usb key to also backup your whole project files onece in a while.