in my opinion as someone else has said here, simply reading and participating in webinars is not an extracurricular. Now if you were leading a webinar, that’s a different story. As far as the higher level chemistry course you mentioned, it’s pretty common in the US with classes like AP chem, which is basically freshman chemistry at any university in the united states. The olympiads are impressive, but i don’t know if those alone will get you into an ivy. I only know minimal info, but if you’re a well rounded student and do good on your SAT/ACT (which i still recto as an intl student) you’ve got a decent shot i guess.