It's hard to tell if your lower back is rounding too much or not, but regardless, I'd sink your hips just a few inches in your starting position. It puts more strain on your legs than it does on your back that way, which is what we want in the first half of a deadlift motion.
One cue that helps me a ton in the deadlift is "wrap the bar around your shins" when you're in the starting position. It'll help lock in your lats and most of your back which (obviously) is key for keeping a neutral spine.
You're moving good weight for a 14 year old. Keep it up bro