You have to actually quit safari. If safari is still open, at the bottom bar of your desktop where all your applications are, a light under the safari icon will be present. If so double tap the mouse pad untill you see a black box with a few options. When you see this hit quit and itll quit safari. After you can then resart the download and it should reach 100% that time.
Called Apple help and they solved the problem.
Showed me how to close Safari