Teaching these days is hard enough without some know it all parent criticizing a well intentioned note.   My daughter is a high school science teacher so I see how much work teachers put in and not being paid what they deserve.   

Just appreciate the fact that your child even has a teacher that's willing to make the effort.

Edit to add I'd say the mistakes come from autocorrect and yes he/she should have checked it closer but some times it doesn't happen.