From my calculation it should be 383. But apparently it's wrong.

You have done computations correctly, but the representation in base 8 is wrong.

45 in base 8 is , thus 37 in base 10; 7 in base 8 is the same as in base 10, thus in base 8 is equivalent to in base 10. Finally, you have , thus in base 8 it is .

Notice that 383 in base 8 does not exists, as digits available are from 0 to 7; 8 in base 8 is 10, thus 383 becomes 403.