Hi,
Why is "TOO" a wrong choice in the following sentence?
I have TOO/SO much work to do, so I cannot meet you today.
'Too' is not wrong. It indicates an excessive amount that is a problem.
I'd be more inclined to see 'so' as inappropriate, unless you change your syntax to say I have so much work to do that I cannot meet you today.
I'd prefer to say simply I have a lot of work to do, so I cannot meet you today.
Best wishes, Clive