If it's not a skills issue, man, I bet the roundabout is too small. I've seen some nice spacious ones and they seem to totally flow.

An airport near my old place replaced one of those 'H'-style on-ramp traffic islands with a circle one each end; then one more very quickly to control a 5-corners to the airport. It was f'n mayhem on day one, but day 30 it was totally smooth sailing. Bam-bam-bam.