"Przepraszam, nasz hotel jest pełny."

Translation: I am sorry, our hotel is full.

[va-diim]

Russian: Proszu prośsienija, nasz oteľ polnyj.

[netis7]

In this case "I am sorry" should be translated to "Przykro mi". "Przepraszam" is also good but sounds less natural.

[Jellei]

I can agree, but the course doesn't teach "przykro mi", so we can't make it the main answer. It's accepted, though.

[Etienne885009]

What do you think of:
I am sorry our hotel is complete! ?

[Jellei]

No, I don't think it means the same thing...

[Ollyfer]

This sounds more as if it was still under construction.

[JanKLinde]

That's a literal translation from French: "Notre hôtel est complet".

[chce_polski]

Captain Obvious: You should've reserved on hotels.com

[Ollyfer]

Or booking.com. “Booking.com—booking.yeah.”

[Karotte17]

Are pełen and pełny synonyms?

[Jellei]

Yes, but the usage of "pełen" is a bit limited, although I'm not sure if many native speakers know it. Without going into details, it seems that "pełny" is simply a safer choice and should be always correct.