Purchased a book from Ibooks but it won't open

I recently purchased a book from Ibooks on my Mac, but it won't open. If I click on it it'll simply show as "downloading" and won't allow me to open it. If I go to it's page on the store it'll simply show as "downloaded" with no option for me to open it. I've tried signing out and restarting my laptop but it dosent seem to work. Would appreciate some help with this.