Sue: The Scots, more than the Irish, are very proud & protective of their first language. Not too shy about letting you know about your errors either.
You sound like a nice person and people have reacted kindly to your question here. A little too kindly even.
If you do not speak the language then where is the point in trying to sing it? Keeping in mind that "Song" is the ornamentation of the words then it's a bit like doing bike tricks before you learn to ride the bike.
There are many fine, Scottish songs which you can sing in your own accent without offending anyone.
Or, you could actually spend the time learning the language but you're not going to accomplish that on a wee holiday trip.