I got some pimples on my face so I visited the dermatologist.

(Sounds good maybe try "I had" instead of "I got" to sound more natural)

(But) The only thing they did was pop some of them and then gave me a prescription.

it took roughly 10 mins.

("Which took roughly 10 minutes" would make it sound more natural and fluid between with the previous sentence)

When I went to the counter to pay for everything, they said the total cost was 40,000won…….omg.

I guess money seems to (just) vanish into thin air…...

(Very good)

My overall comments: you're already a very good English writer compared to most Korean people. Keep practicing and you'll become a professional in no time!