1. Literally: “I was sorry about not being able to go.”
If, however, you’re sorry now about something that happened in the past (not being able to go), we would say “I’m sorry I couldn’t go” or “I’m sorry about not being able to go.”
Note that the word “ci”, meaning “there”, is not translated.
2. I’m sorry you can’t come. (Or, "I'm sorry about your not being able to come.)
Note that English doesn’t use the subjunctive in this type of sentence.
In general, use “I’m sorry that + A. subject + conjugated verb in the indicative.
I’m sorry that she couldn’t come.
1. Same person: subject + gerund
I’m sorry about not being able to go.
2. Different person: subject + possessive (or, colloquially, object) + gerund
I’m sorry about their (or “them”) not being able to go. (“Can” is a defective verb, with no gerund, so we substitute “being able to”)