First:
Every ectomorph I've ever met has had to eat a lot of food to move out of the catabolic zone.
Remember...
You need to be carrying plenty of muscle on your frame if you want your body to produce optimal levels of testosterone.
To get that muscle you need to down more calories than the average Joe.
Second:
Anaerobic exercise must be your friend, and aerobic exercise your foe.
I argue all over my site that aerobic exercise is a catabolic activity, and this is especially true for ectomorphs.
To make the shift from catabolic to anabolic, eat plenty of high quality food, and focus on explosive, high intensity training.
Training done in the weight room, with an emphasis on heavy, compound exercises like squats, deadlifts, and military press.
And remember...
Since you have a natural inclination toward a catabolic state, it's absolutely critical that you do not over-train.
20 minutes of sheer insanity in the gym, three times a week, followed up with plenty of food, sleep, and recovery.