In my opinion, you have done a positive thing by agreeing to do more teaching. I am incredibly shy and used to feel extreme discomfort talking in front of more than one person. However, I too started teaching this year and can honestly say my confident grows weekly. I felt physically sick when I initially agreed to it, frequently thought of cancelling. Now, I know it was one of the best things I did. Yes, I have had slip-ups and embaressments in front of students but - so what, they leave that room and probably never think of it again (the embaressment that is!). They probably don't even notice half of it.
On another note, I have had most students say they enjoy the seminars and others who look as if can't be bothered- you really can't please everyone.