Sounds like you might have turned from a lane that wasn't a turn lane for the turn you made, IE: made a left turn from a right turn only lane or a left turn from a straight thru lane only. Being a warning, move on down the road, try not to make the same mistake again.
As for the correct lane to be in, cdreid has it like I do it. Turn from the farthest lane you can legally turn from for the turn your doing. This gives you the widest possible angle to turn. If it's a tight city area, try the button hook turn instead of swinging a little into the lane beside you. Case being, if you get together with a stupid 4 wheeler, you could be charged for making an improper turn. The button hook means you take the cab into what would be the oncoming lanes halfway thru the turn as your doglegging back. Here's a button hook:
http://bikeportland.org/wp-content/u...odot_turns.jpg http://s1.hubimg.com/u/1524540_f260.jpg If traffic is an issue, wait till they move. If need be, park the truck in the middle of the intersection until they move enough out of your way to finish the turn.
Swinging into the lane beside you means your opening the door for 4 wheelers to attempt to slip thru and this is the end result:
http://standardspeaker.com/polopoly_...3857056264.jpghttp://www.truckdriversnews.com/wp-c...n-accident.jpg