Liquid calories. It's an quick and easy way to get calories in. Drink whole milk. 1-4 litres a day. 2 litres is over 1100 calories and doesn't require any prep and a litre can be drunk in minutes. You can add nut butter, protein shake, olive oil, bananas to it for more calories. I can drink 1000 calories in one shake.
Stop giving yourself labels such as extreme ectomorph and hard gainer. You just don't eat enough. Eat 3000-5000 calories every day and lift weights for the next 5 years and you won't be calling yourself a hard gainer.
Also, someone of your weight shouldn't be worried about fast food or pizza. I wouldn't limit yourself right now.