There are two main reasons for your Scottish Tablet burning in the pan and that is either you aren’t using a heavy enough pan or alternatively you aren’t stirring it enough.
The pan you use needs to be large and have a heavy base because you are heating the mixture to such a high temperature. The volume of the mixture will also triple as it comes to the boil so if you don’t have a large enough pan to accommodate that you will get a very messy cooker!