Backup your belonging. Opt out all Betas, wait some second quit steam and may also restart you pc :) log back in to steam if there is still no download go to egs properties in the library and verify the game installation.
The process of downgrading playing and opt out to actuall public stable works just fine as i tested it bevore.
If nothing helps try uninstall the game then again egs properties in library and opt out - restart steam and reinstall