Hi M.,
I think the important thing to remember here is that his schedule is something YOU need to lead - bedtime and naptime are when you say they are, every day. As long as you are very consistent with your routine, your son will do what you ask of him.
That being said, I definitely think you need to cut out the TV time before he goes down for a nap. I think they get way too wired when they watch TV and it takes them much longer to unwind.
With my daughter (who is also 3), we keep her routine the same whether she is in preschool or on the weekends - she eats her lunch at 11:30 and then she lays down for nap at noon. We keep the room as dark and quiet as possible (although for my older daughter, she used to like to listen to quiet music and that worked out fine too). I tell my little one, "You don't have to sleep, but you do have to lay quietly in your bed." Sometimes she asks to take a little doll or book to bed, and I let her.
The point is, you're at a time in your life when you need him to take a nap, whether or not he feels like it. Since you're the mommy, you get to set the schedule! Stick with it, and he will fall in with what you need from him. He will likely resist for several days, but soon he will see that you say what you mean, and he'll get with the plan.
Hang in there, and good luck with your little-one-to-be!