1: For a quick fix install DaisyDisk or any other app that can easily tell the size of the SSD folders go to private
2: keep looking folder with the 12GB size above you can have the copy of the Xcode download from the App store and make a copy of it xxxx.pkg to your desktop below is mine
3: Use Activity Monitor to cancel the pending install process (Force Quit) note this will automatically delete the downloaded Xcode file from the App store so open the copped file to confirm if it Xcode before (Force Quit)
4: Now open the copy of the Xcode file in Step 2 to start the new installation process