I think you should call the admin and tell them that you do
not think you can do the job successfully and asking them if
they will release you from the agreement. But first, do the
following first thing tomorrow...
Call the local teacher's union and ask them whether a letter
of intent is legally binding (even if they don't represent
you--they will still know the answer). Also call Colorado
Department of Education tomorrow and ask them the same thing.
I think you are smart to see early that the working
conditions might be bad.
Many charter schools are just basically low performing
schools in disguise. In general, low performing schools are
dysfunctional and can have unfair, abusive, and unrealistic
expectations and conditions for teachers.
By the way, what do your duties include?