Driving roundabout lane query Help please

http://imgur.com/iuIjTVi (Diagram of the roundabout)
The road the red car joined from is a dual carriage way, followed by round about then a continuation of the dual carriage way.
Hi,

Recently passed test, was out driving on way home from work.
Was out driving with my dad (who has been driving for many many years).
I was in the right hand lane (shown in blue) and was taking the 3rd exit onto a dual carriage way. The red car joined from the 1st exit i drove by and when I did my mirror check and saw the car but decided to then take the right hand lane on exiting and accelerate past them then move back over (checking it was safe to move back to the left hand lane).

Questions
1. Should I have went back round the roundabout?
2. In normal situation I would normally exit onto the dual carriage way into the left hand lane is this correct?

thanks
claire