i'm having trouble getting music to load completely on my iphone i purchased.

Welcome to the Apple Community.

Try deleting the problematic file (electing to remove original file if/when prompted) and then re-downloading the file from the iTunes store.

You can re-download content purchased from the iTunes store (availability varies depending on location) using the purchased option from the Quick Links section in the top right corner of the iTunes homepage in your iTunes application on your computer.

You can re-download content purchased from the iTunes store (availability varies depending on location) using the purchased option at the bottom of the screen of the iTunes app (or video app) on your iOS device.

If the problem re-occurs, select the content which is causing a problem and use the 'Report a problem' button in Your Purchase History using your computer.