If your WES is measured against a US degree (then it should be fine), I wouldn't bother with extra schooling before actually trying to get a TN with what you have. If your Indian degree is equivalent to a US bachelor's degree, then whether it is 3 year or 4 year doesn't matter: It is equivalent to a US bachelor degree.
Was your WES eval measured against a US degree or against a CDn degree? You would need to have it measured vs. a US bachelor's degree in the field of study. If WES says it NOT equivalent to a US bachelor's degree, then you have a problem.