I think virtual teaching is hard and please don't worry we are all in the same boat. I think I have started every lesson off with 'Can you hear me?' and 'Can you see my screen?!' and have repeated myself several times! 

One thing which helped me was to have Mel in the lesson, not necessarily to teach although his computer knowledge is legendary!! It was to have someone else in the 'room' who could feedback as the whether or not my screen was showing or if anyone could hear me. We even had a bit of fun dialog.

Another way to achieve a similar result is to nominate a student to be your 'Mel' in the lesson. It made the teaching fun :)