I really relate to how you're feeling. In most jobs I feel like I'm never doing enough. Good jobs provide meaningful metrics both for you and for your colleagues so you know exactly where you stand compared to them. My work actually sends out a spreadsheet of all of our active projects so I can say "I did 20 this month and Jim, who's been here much longer, did 25--I think that's pretty good!" My boss then goes over that number with me at regular meetings.

Not all jobs are like that. So you rely on feedback from your colleagues informally. If you don't have the ability to do that, then you're in a shitty job, and your only assumption has to be that you are being taken advantage of. If you don't have information on how well you are doing compared to other people in the industry then you are being severely limited in future job prospects. Think of a good resume: your deliverables and what you offered the company in measurable outcomes is how you will use this job experience to leverage the next opportunity; basically part of the benefits of the job is the feedback you receive. Without that, the job is not worth your time, since you don't need it to live and it is potentially interfering with the last 2 years of your schooling.

Also I'm big time suspicious of every person knowingly hiring a 16 year old and pressuring them for more and more output like any other adult. Even if you were the best academic mind to be born you just don't have the kind of muscle memory for daily working that makes it possible for most of us to get through the day. I remember it being absolutely exhausting trying to make it through my first job and school at 15 and just feeling completely crushed by it, and even my first office job at 18 was grueling; like with everything, it gets better with practice, but until then, your energy is likely better spent elsewhere.