But you cannot position planets to be like a bottle neck? I did read the tutorial about map designer unless I missed something?

There are actually two ways to make maps in Sins and should not be confused with each other, as they make totally different maps.

The in game map designer is for random maps, where you can customize parameters but the map you play will be different every time, making it impossible to make specific choke points.

The Galaxy Forge is an external program made by the devs used to make custom maps, and these will always have the same layout, with many other options thus available not in the map designer. For Rebellion, it is located in your Sins install directory, in the steamapp folder. For all other versions, download it from the downloads section of this website.

As for choke point maps already in game, Douplegangers is a good one, each player has a small solar system to themselves. You don't get much better chokepoints than stars if you really want a long game.

If you are looking for a somewhat similar map by default in Single Player, Gateway is probably the closest you'll get. You start off like in any other map, and your opponent can get to you as easily as any time else, but rush the tech for between stars jumping and you can travel past planet "Gateway", for which the map is named, through its parent star and into the other system. This is the only way to enter the other system - through the planet gateway. Hold Gateway [Or the star beyond thanks to Starbases], and you control the entire other star system [Most likely], and your enemy has to push through the Gateway chokepoint to get to your empire.

No maps that will start you off on a planet with just 1 jump leading out of it though.