Migration Assistant

I recommend starting over. In my experience, doing a Migration Assist transfer only took about an hour or so. It could take longer if you have a lot of data. The app is very easy to use and works very well if done correctly. (Follow the directions.) Be sure to first set up your new Mac. When It asks if you wish to transfer data, click yes and then connect the two computers with a USB cable. Do not use Wi-Fi or Ethernet. (I'll bet you did and that's your problem.) Next select the groups of data you want transferred. The new OS in the new computer will not be replaced.

Use Transfer Assistant during the actual installation. Migration Assistant is an app for moving data afterward the first install and creates a new user account. It then makes it difficult to look at old data on external disks etc because it gives permissions problems.