Yes you are correct, on is not appropriate in this context. In fact to my ear at is a little problematic also in this sentence as it suggests at a particular place or time and the lesson is neither. I would restructure the sentence to - Your teacher will be waiting for you tomorrow for your lesson or Your teacher will be waiting for you tomorrow at 2pm for example

As teacher Jan said, this is a mistake. Non-native speakers, even if Engish teachers in their own country, have trouble with prepositions.

I would be cautious about taking English lessons from a teacher that made such a fundamental mistake. That said, learning how to use the correct preposition in English can be difficult. There are prepositions of time and place, preposition-verb collocations, and phrasal verbs. All use prepositions in ways that are difficult to translate into other languages. Here's a good resource to get you started: https://forum.duolingo.com/comment/11581297/In-on-at