Try to re-download the entire zip and see if that helps.
You can also try a different unzipping software if it still doesn't work.
You might also try unpacking it to a different folder on your computer.
(It is correct that there should be a "FPVFreerider_Data" folder next to the executable).
As for the email address, please email support@itch.io. They handle all the downloads/purchases, I'm sure they will be able to help.
(Here is some more info on purchases etc https://itch.io/docs/buying/al...)