Test-driving an old car

I'm looking forward to my first interaction with a class of undergrads for quite a while. I did not do any teaching as a post-doc, and since there are almost no training opportunities for perspective faculty members to improve their teaching unless they convince a department to let them teach all or part of a class at the expense of their real reason they are getting paid (research), I don't have a lot of experience teaching outside of TAing as a grad student. I took a few touchy-feely educations courses as a grad student and a three day teaching workshop when I got here, but does that really prepare you for standing in front of a room of 19 year olds and convincing them that what you are explaining is actually interesting to them? No. So, today will be a good test drive for me. The lecture is on a topic that I know well, so I put the slides together yesterday (well, mostly. I still have to finish it) and we'll see how it goes. Can I slow it down so that they can the main concepts? It is not like a lecture to your peers, which is what I have been doing for the last 10 years, but a completely different kind of presentation. Will they walk out feeling overwhelmed or like they got what I was telling them? Can I hold their attention or will half the class be texting their friends after 20 minutes? I guess I will know in a couple of hours....