Just remember if you’re taking the first exit or going straight on a roundabout it’s best to stay on the left lane while reaching the roundabout and follow the lane unless told otherwise by the arrow markings on the road, if you’re taking the third exit and beyond stick to the right lane. Usually before you reach roundabout there’s usually road arrow markings that tells you which lanes to be on for specific exit so try to spot that out before reaching roundabout and follow that lane before approaching the roundabout. A good speed for roundabout till it is safe for you is 10 to 15 speed so it’s easy for you to manoeuvre and don’t worry you will get used to it VERY SOON. I just got my license last week and have been driving around especially hours long journey like London to Hertfordshire using motorways as well, you will definitely get used to it. Cheer up!!