A wave packet is built from many momenta, like a chord is built from many notes. To make it narrow in position you must add a wide band of momenta — and vice-versa. The two spreads are a Fourier pair, so squeezing one forces the other to grow.
Their product has a hard floor: σx·σp ≥ ℏ/2. Here ℏ = 1, so the floor reads 0.5. You can sit exactly on it — a minimum-uncertainty packet — but never below.
This is not a clumsy-measurement effect. The particle simply does not possess a sharp position and a sharp momentum at once; the spreads are a property of the wave itself.
Let a tight packet go and it disperses: its many momenta drift apart, so σx grows while σp stays put and the product climbs above the floor. A tighter start means a wider momentum band means faster spreading.
Something in the simulation stopped unexpectedly — the lesson continues without it. Nothing you did was wrong; you can move on.