Scotch, Scottish, Scots can all apply to what constitutes, belongs to, or derives from Scotland or its people.
Scotch is most widely used outside Scotland, especially in the spoken language.
Scottish has a more literary, less casual flavor and use.
Scots is used in the same way as Scottish except that Scots is sometimes preferred in reference to law and in historical references to money. In Scotland itself Scottish and Scots are often preferred to Scotch , but Scotch also is used, especially with regard to the products of Scotland.