Help! How can I make my chest appear flatter?

hello everybody, hope you're doing well! I'm a cis bisexual girl and even though my chest isn't that big, I'd love it if it were totally flat. I don't want to get surgery (also, I'm just 18 yet), and I can't buy a binder without my mum knowing (I don't want her to know), so how can I make my chest appear flatter and how can i dress more masculine in a hot weather? thankyou!