Which is Worse?

What's worse, not eating enough calories, or getting calories from less healthy foods?

I can't seem to get to 1600cals every day without eating some less healthy foods, so should I just stop eating when I'm full, or add some extra calories from a little bit of junk food? By the time I finish dinner, I'm usually up to about 1200-1400cals, which is less than the minimum for my age, and I'm scared of going into starvation mode (I hear that can happen at 1200).

It could be that I'm not measuring my portions very well, but I don't think I could be more than 100-200 calories off.

Maybe try adding things with oil in them, such as olive oil (dipping some bread in oil and herbs is really good - it tastes better than it sounds) or peanut butter. Fruits and juices are packed with calories too. Try finding something that you enjoy. Eating junk can lead to unhealthy cravings, so just be aware of that if you choose to do so. Overall, moderation is key. You don't want to go too overboard in either direction. Eating enough calories is so important, especially when you're young, because your body needs that to stay healthy and develop properly. To answer your question though; yes junk is better than nothing, but healthy higher-calorie foods are better than junk.

If you don't continuously lose weight then I'd say it'd be better to settle for less calories from healthier foods.  However, if this is not the case and you need calories to maintain then I'd say that your false dichotomy fails.

You can get plenty of calories from healthy foods, don't try to fool yourself otherwise.  Olive oil, peanuts, almonds, cashews, walnuts, cheese, avocados, blackstrap molasses, humus, etc...  The list is quite big.

Another trick is to add a few more calories earlier in the day.  Try adding an egg, or a tablespoon of peanut or almond butter, or an extra glass of milk to your breakfast.  Try adding some olive oil and some nuts to your lunchtime salad, or some hummus to your sandwich.  If you have a mid-afternoon snack, you can add some protein or fat to whatever you normally eat. 

Adding another 100 calories to each of your meals isn't hard to do -- I mean, isn't that how most of us gain weight in the first place?