It's normally in the same system as you started in, one station over. If you look on the system map, or even the galaxy map you will see a blue icon next to the name of the system (galaxy map) or station (system map) - this indicates where your ship is hangared. Go to to the station, dock (remember docking permission!) and select shipyard from station services. You then click on stored ships, and you should find your ship (Eagle)