In itunes is there any way to select multiple songs to send to itunes library?

I just mixtapes from datpiff and the only way i could put it in my library was to select manage songs manually under my devices. I didn't know that it would delete my songs from my iphone to put that on but it did. I only have songs from itunes, not beemp3 or datpiff.luckily all my songs are saved under the music file and its 319 songs. Is there any way i can select all them to put in my library? I know about the hold shift trick but its not working.

What you do is, scroll up to the top song, while holding down the "shift" key, click the top music file ONCE to highlight it, then scroll to the bottom (while holding shift the entire time) and click the bottom music file, then all other files should be selected at once. Then right-click any file (or control-click if you're on a Mac) and click "open in iTunes" or something along those lines.
If that doesn't work - use the other "shift" key, because who knows, maybe ol' reliable is unresponsive now.