Three weeks until an assignment is due sounds like plenty. Once sport training, music lessons and everything else in a normal week are in, it usually isn't. Fill this in and find out now, not the night before.
Copy the title straight off the task sheet.
What's on each day — sport training, music lessons, anything regular — and how long you could really work afterwards. Be honest: if you're wrecked after training, put none.
Dinner at Grandma's, a birthday, a weekend away, a carnival. Add the date and it comes out of your available time. This is usually where plans fall apart.
Nothing added yet.
Your steps, your estimates — nobody can do this bit for you. Reading the criteria sheet properly is always step one.