Recently passed driver - confused about a local roundabout

Hi all,

I am awfully confused by a local roundabout and would appreciate your thoughts. I have described the situation below and would like to know which of the two approaching lanes I should take.

1. Upon approach to the roundabout the round sign indicates three exits. One to the left, one straight on and one is a full 360 and back off the roundabout
2. As you approach the roundabout there are no instructions as to which of the two lanes you should occupy in particular. (left is not for left only for example)
3. I wish to take the second exit, going straight on, exiting into a single carriageway.

My confusion arises from the fact that the round sign has positioned my exit just past noon. I have been occupying the left hand lane for my desired exit as it was my understanding that in the absence of road signage telling you otherwise that the left hand lane is for left and straight on. My concern arises from 1 or 2 cars trying to take this exit from the right hand lane. As there is only a single lane for exiting this becomes problematic.

What are your thoughts? Am I in the wrong or should I keep on doing as I am doing?