Roamnia - I have 4 full days in Brssov, too much?

I booked Brasov just to relax, but I change my mind now and wanna move around. I think ill be bored with 4 full days. 1 day is enough to see the Peles Castle, 1 day is enough to see old town, i was to skip the other castles because people say its not worth it. Im not interesred in hiking . Should I do a train ride to Sibiu nearby? sounds exhausting though because I need to be back at Bucharest for my flight