Some folks have been struggling a bit with the server install of the Beta.  PowerPivotGeek has some updated steps here that should help quite a bit:

https://powerpivotgeek.com/server-installation/ 

Also, VidasM has been a busy beaver as well, running multiple installs, troubleshooting, and helping others.  He’s summarized his findings here:

https://www.powerpivot-info.com/post/66-step-by-step-guide-on-installing-powerpivot-for-sharepoint 

Enjoy!