I'm not sure if you are an ectomorph, but whether you are eating enough or not is the question. If you are not gaining any weight the answer is no. Do you eat 6 times a day? 3 major and minor meals? Even ectomorphs do well on a high calorie diet. To gain weight you should always be on a calorie surplus diet. Do you consume enough protein? If you are a vegetarian you will have to find ways to consume enough Protein to gain muscle mass.
Your question reveals a few things:
You need to understand 60 push-ups doesn't necessarily mean you are strong at everything. You do have endurance for push-ups but how much can you dead-lift? Strength is a very relative term for many people some consider themselves strong when they can run 10 miles without puffing. Not all forms of strength mean that you will look big or have extra mass. Consider the marathon runners who are mostly skinny.
What you mention as shape while gymming is nothing but temporary hardness of the muscles that most beginners experience. Given that you already mention that you are skinny what is great shape anyway? I am sure you lose this shape in few weeks if you miss going to the gym. The temporary hardness is a "pump" effect that occurs when muscles become engorged with blood and is felt by beginners and long-time lifters.
If you have never done any gymming before I suggest you to start with a strength training program first. This includes 3 days a week of full body workouts with 5 sets of 5 reps for each exercise. There are a lot of good programs like Starting Strength, StrongLifts, etc. They will definitely help you bulk up. A full description of these programs and proper form of the exercises will be difficult to document in this answer. These program basically focus on getting stronger with a few basic moves; getting bigger is a side affect. I recommend you to search for these programs and follow them judiciously for a few months before you conclude that you eat enough or you are an ectomorph.
One more point I would like to make is, it is easy to feel that 3 days is way too less work out but please note muscle size is a function of exercise, nutrition, and rest. If you work out alone that will not increase size so please follow the program as Rippetoe says.