I don't think you have enough fabric to do an historically accurate great kilt. According to most sources the plaid was about six ells of double tartan-- in other words it was about 5 feet wide and about 18 feet long.

If you have a kilt that matches your length of fabric, you might want to consider making a "top piece" that would give the impression of a great kilt, and which could be removed during the lecture to show how the kilt was transformed during the 17th century.