Firstly, uninstall the Alpha client.
Secondly, navigate to C:\Users\YOUR_NAME_HERE\AppData\LocalLow, (or either ~/library/caches / /Users/NAME_HERE/Library/Application Support/TSBGAMING on Mac) then delete the TSBGAMING folder.
Thirdly, re-download the Alpha client and then add the installer as an exception in your antivirus before launching it. Before you claim not to have an antivirus - yes you do. All Windows PCs come with Windows Defender pre-installed, which is embedded into the operating system making it impossible to remove.
And finally, re-install the Alpha client by launching the installer.
Note that download times are user-dependent. It is affected by things such as internet speed, ISP throttling, available system resources, and so on. Be patient, there is nothing that The Sandbox can do about these user-sided factors.