Can't download itunes album purchased on a different computer to Iphone

I purchased an album this morning on my laptop at home. I got on the bus and realized that all of the songs hadn't downloaded. I logged onto itunes at work and the album shows up under purchased music, but it won't let me download it to my music on my iphone. I've authorized the computer, I've checked that the purchase isn't hidden and I've tried to drag and drop the album into my music. It will pull over to there and it shows the little plus mark, but it doesn't download it to my music. Please help! I can't figure this out.