The answer is don't worry about it, you can come and go as you wish.
Hopefully you noticed last night that when i noticed a message request (you couldn't see it) from Brigitte that i added her to the conversation and we carried on.
While i did this the others continued conversing, so there was no interference with what was currently happening.
The blue border is part of the system to highlight who is speaking now, and you will soon start to ignore that because you are to busy listening or speaking or thinking.
The important and i think very useful part of these skype sessions (i have to keep reminding myself) as i hope you found last night is the normal SSIW idea of just let go and take part, everybody ran out of words at times and others helped with that.
I made mistakes and should be better than i am, but i didn't notice anyone worrying about it, i did look up 'Cam' and now remember it means mis as well as step. You may feel you are struggling just as much next time, the important bit is it will be with different problems, so you will be moving forward ( heb sylweddoli) without realising. Enjoy dy gymraeg.