iTunes library problems

I'm running iTunes 12 in Yosemite. My iTunes library was a mess. It was a mix of albums, partial albums, singles etc. with no cohesive order - this took place over time due to my laziness/stupidity in not keeping things organized.

I decided to revamp the whole works and built a totally new library. I searched for ways to delete the old library but have only found ways to re-create it in the Apple support pages.

I tried recreating and also tried reinstalling iTunes with it pointing to the new library. But even with 'only music available offline' checked I keep having occurrences from the old library show up in the new one.
In the new library I have created some 'albums' more or less various songs of the same genre from different artists that were single songs scattered throughout the old library. Rather than having them show up as an album, they populate iTunes in their old 'single' iterations.

Is there any way to start with a clean slate in iTunes? I don't want to use iCloud, or any other such streaming. I would just like to group my songs and albums as I see fit. Any help with this is much appreciated.

BTW my library is about 60GB if that matters.

Thanks

Dave

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