Cancelled wireless Migration Assistant... best way to start over?
If the destination MBP is brand new, save yourself some trouble, restore it from factory and run the Migration Assistant again.

However you can probably run it again and everything should be ok, it really depends what you have and what has been copied. Check /Library/ and ~/Library (use the Terminal), for example if you had GarageBand or Garage Band Jam Packs, those may have been partially copied. 

I did that when I brought an MBAir. It was taking so much that I aborted, cloned my other Mac's drive and used a USB drive to do the migration.