Well, that's easily a dodgy situation if there's other road users around, so best thing would be to just take a safer/earlier exit.

If you're set on taking the right exit then definitely signal right as if you were in the right lane. The main priority is to tell cars waiting to join the roundabout not to pull out on you. Cars already on the roundabout are a danger that can be avoided by watching out. People to your right and behind aren't an issue unless they speed up to or past you. People to your right and alongside/ahead of you need to be watched closely - they are likely going after the same exit as you are BUT might want to take an earlier one and might not see you - just give them room to move over at each exit and you'll be fine.