During your next 2 years, choose science and mathematics as your subjects. Some schools also offer programming languages (C, C++) as additional subjects so you can opt for them as well. Please keep in mind if you want to go for a formal undergrad course in software engineering after your school, you would need to be prepared to meet eligibility criteria and also clear entrance exams of your choice of colleges. Mathematics and programming languages will help you to have an added advantage.
These days different schools and companies also organise programming competitions (Called Hackathons), you should start participating in these after you have learnt basic programming skills.