Don't sell yourself short. I've taught college in the U.S. and your writing -- although not perfect (nothing is incorrect, there are just little tells in terms of idiomatic sentence structure and comma use) -- is easily within the range of native English speaking college students, especially in STEM fields. I'd also say it's notably better than most J->E or K->E bilingual students I've seen, so extra congratulations for your fluency given the fairly difficult language gap between Japanese and English. :)
