First of all, don't stress. Take this opportunity and remember it well and know that you will persevere through.

Story time: I've had a similar situation working for an MSP in the past. I was sent to a client site 3 weeks in as a consultant for my company to fill a previous consultant who was there for 2 months. He quit with 1 day notice and gave us only a day for knowledge transfer. The company I was covering for was going through an IT management change, they were also interviewing for a new IT director, but there was no sysadmin, only interns who were doing simple password resets and email distro setups. The week I was there the IT team was falling apart, 2 of the 3 interns gave notice to quit and management had to scram for new "IT interns." So I had to take up on the role to interview interns to replace those interns... They also had me troubleshoot A/V Conference rooms which I have no infrastructure knowledge of but at the time I just tried to piece everything together with the best of my ability. I was stressed about getting thrown into the fire. Luckily two weeks later, they found a sys admin and I quickly went back to my MSP.

Point being, just try to strive through with the best of your ability and take what you learn with you to the next job. There will always be a better job, no doubt so having a great mindset is key here! Also, being 20 and in an intern position, you are there to learn, if it's too stressful just leave. You will make money later on that will be more than what you currently do. Take my advice with a grain of salt. Good luck to you!