ShotPro currently does not support retina display, however you can use third party resolution switching apps to achieve the same effect. One of the apps that we recommend is "Display Menu". It is currently free on the Mac App Store.
Once installed you can easily switch the resolution, so that you can take full advantage of the high resolution display of your retina machine.
Then in ShotPro you can adjust the UI size to your liking by pressing the two arrow buttons in the help menu.
You can also adjust the Cursor Size and the Tracking Speed by going to Settings of your Mac and clicking Accessibility or Trackpad.