I’ve merged your two topics because despite being separated by a week, they’re roughly the same.
Please don’t create more topics asking for preparation material. If you haven’t gotten a satisfactory answer to the others you’ve posted, asking again won’t change things.
I think you’re already doing the best thing you can do. Coding with other people, making stuff, challenging yourself and having fun are great steps. Whether or not you get a job at a startup depends on too many variables for anyone to say, but just do the best you can and send your resume out to as many different opportunities as you can.