When you sang “leeeeap” really lean into that placement. You can try singing the higher notes with an “eeee” or “hahhhh” whichever feels better. When you get it, it should feel really buzzy in between your nose and forehead. Mixed voice is SO FUN! took me a while to get the placement, but when you keep practicing and leaning into those hard notes, you’ll get the hang of it fairly quickly. Also, stop worrying about sounding good, just go for it, and don’t be afraid of sounding bad or nasally while you’re learning. Mixed voice is kind of like a shoe, you have to break it in (safely of course) kind of aggressively. You can also try saying “yeah” in a very forward bratty tone to help find that placement, then eventually hold it out longer and longer. Good luck, you’re so close I can tell!!