hi shafzy,

for the round about, the roles are:

3 lane circle

want to go right: enter right lane exit right lane (stay in same lane when exit)
want to go straight: enter right or middle lane, exit same lane as you entered
want to go left: enter left lane, exit same lane

2 lane circle

want to go right: enter right, exit same lane
want to go straight: enter righ, exit same lane
want to go left: enter left, exit same lane

as a general role, always exit is same lane you entered, that is do not change lanes when exiting.

good luck