Device already associated with an Apple ID?

I recently had had my sister sign in to her apple id on my iPhone, i downloaded a few songs, and then signed back into my ID. But now, multiple songs of mine are set for iCloud download. But, when i click to download them back, it comes up with a warning stating "This device is already associated with an apple id. If you download past purchases with your apple id, you can't auto-download or download past purchases with a different apple ID for 90 days" And it gives me the option to cancel, or transfer. If I click transfer will it delete my songs, or what would happen?

Yes you will lose your music. Apple designed devices to only be signed into one Apple ID per device at a time per 90 days. You can contact Apple Support and have them talk to iTunes about removing the lock but other than that, the device belongs to your sister's Apple ID until that 90 days passes. You can still download your past purchases if you are signed in but if you sync, your sister's stuff will be on your device.

Obviously a phone can only be identified as one device.