"I am really sorry!"
Translation:Jeg er virkelig ked af det!
I would say that rigtig can mean really, but in the sense of truthfully, and spreaking of discernible characteristics. In this case is virkelig, since it is an emphasis of one being sorry, translating perhaps more closely to "I am very sorry!"
I have never seen "undskyldende" in this course, but that was how my sentence (Jeg er virkelig undskyld) was corrected. Does anyone know why?
Same just happened to me. I also wrote - Jeg er virkelig undskyld. Someone please explain!
"I am really excuse."
That doesn't work, either.
undskyld! is the command form of undskylde in much the same way that "excuse!" is the command form of the verb "(to) excuse".
You can say "Forgive me!" or "Pardon me!" or "Excuse me!" or "Sorry!" -- but though you can say "I am sorry!", you can't say "Sorry me!" or "I am forgive!" or "I am pardon!".