I'm sorry I couldn't help you. / I'm sorry I wasn't able to help you.
"be" removed :)
I wish you had told me you were full. / I wish you had told me you had eaten.
one "you" removed
"full" means eaten and cannot eat more.
"eaten" does not imply eating a lot. It uisually means had a meal, so assumed to mean adequately.
As a consequence these would be used differently.
Have you eaten? asks whether you have had a meal, equivalent to being hungry. So you might ask a friend arriving about a meal time.
Are you full? Makes little sense for a friend just arriving. Instead, equivalent to asking whether they have eaten anough, hence as when offering even more food.
So, Difficult to create a situation when you would need to use "I wish you had told me you were full. ":)
As if you had been trying to get them to eat more for an hour and failed.