Center point is off when I use JavaScript for animation creation.

I’m not sure which code you used, but attached is a .story file that compares different options and approaches:

Example 1:
Object is rotating with the Default Spin Entrance Animation

Example 2:
Object is rotating using a JavaScript API object reference and the Web Animations API

Example 3:
Object is rotating using a JavaScript API object reference with the rotation property and update() function

/*
  JS - Locked Centered Continuous Slow Rotation Animation for Oval 1
  Animation Details:
  - Oval 1 rotates 360 degrees in 5 seconds.
  - Rotation is locked around its center.
  - Animation repeats indefinitely.
*/

const oval = object('5nl2b3u6wAP'); // Oval 1 object ID

// --- Initial Setup ---
oval.style.opacity = 1; // Ensure the oval is visible
oval.style.transformOrigin = '50% 50%'; // Lock the rotation point to the absolute center

// --- Continuous Rotation Animation ---
oval.animate(
  [
    { rotate: '0deg' },          // Start at 0 degrees
    { rotate: '360deg' }         // Complete a full rotation
  ],
  {
    duration: 5000,              // 5 seconds per rotation
    iterations: Infinity,        // Infinite repetitions
    easing: 'linear'             // Smooth, continuous rotation
  }
);

This is the Code created with Storylines Assistant.  

Rotates just fine with this script from ChatGPT.  

if (obj) {

const rotationSpeed = 360 / 10000; // 10 seconds per rotation

let lastTime = performance.now();
let rotation = 0;

// Capture Storyline’s original transform
const baseTransform = obj.style.transform || "";

function rotateGraphic(currentTime) {
const deltaTime = currentTime - lastTime;
lastTime = currentTime;

rotation += deltaTime * rotationSpeed;

obj.style.transform = `${baseTransform} rotate(${rotation}deg)`;

requestAnimationFrame(rotateGraphic);
}

requestAnimationFrame(rotateGraphic);
}