When I Borrowed My Little Brother's Toy Without Asking

So here's the deal. You know when your younger siblings get new toys and suddenly they seem more interesting than anything you've ever had? Yeah, that happened to me last week. My little brother got this super cool set of construction blocks for his birthday, they look like mini Legos but with a twist. He was all over them like crazy, building castles and towers and stuff. I thought it would just be a phase, but after two days, he still wasn't putting them away. Meanwhile, I was sitting around feeling bored out of my mind because all the other toys look old to me now. Now, I know better than to just take something without asking, especially when it's a birthday gift or brand new toy. But there it sat, right next to his bed in plain sight. And let's face it, he doesn't even sleep with that thing anymore; it's basically like it’s abandoned. So one day, while he was playing outside, I just took the blocks and hid them in my room. I figured I'd put them back before he noticed. But here's where things get tricky. Once I had those blocks in my hands, I got way more into building than I thought I would. It’s been days now and there hasn’t been a single moment when I wasn't thinking about that set, or feeling guilty for taking it. Every time I hear him coming home from school, my heart races because I know he'll want to play with his blocks soon. I’ve tried hiding them in different spots around the house, but it’s not really working since we live in a small apartment and everyone can see when you’re doing something weird. Plus, every time my mom asks where the blocks are, I feel like she’s looking right through me. So now what? Should I just tell him that I took them? Or maybe buy another set for myself as a replacement so he doesn't get mad? It's been driving me nuts trying to figure out what to do and how to say sorry. And honestly, part of me still wants those blocks back even though deep down, I know it’s not right.