Navmesh agent miss destination

I am not a pro with navmesh agent. Just saying before someone will bash my skull in :p

The thing is. I dont have a problem giving my agent a destination. The problem is that my agent often miss the destination when it is going in a curve and then it turns back to get to this destination. Sometimes it misses the destination on its way back. This could be a problem for me since i dont want the agent to go outside an area where it is not allowed to be.

Am i handling this agent wrong or is this just something that will happen sometimes for every agent. Is there some kind of optimal speed and acceleration and so forth that i should use to make the agent not miss.

Or should i just make my own a* pathfinding?

How my game works: http://cdn3.steampowered.com/v/gfx/apps/228960/ss_c0e05df5dbbab3510348998f714abc27d7e2e2db.1920x1080.jpg?t=1375739623

Look at this picture of the game skulls of the shogun. The units in that game has a white line where it can move within. My game got that aswell and the destination can not be set outside this line. But the car misses the destination and run outside this area.