.addCustomItemsToCart() runs every time I open my cart

I’ve been trying to set my store up in a way that charges my clients an extra $10 whenever they customize products by adding custom text, so I’ve added the following function to my Cart page:

import wixStores from 'wix-stores';

const customization =
        name: "Customization fee",
        price: 10,
        quantity: 1,
        note: "Each customized product costs $10 extra!"

 .then((updatedCart) => {
 const cartId = updatedCart._id
 const updatedLineItems = updatedCart.lineItems

The problem is, every time I go into the Cart page, the function starts running and their total is increased by 10. So if they buy 1 product, but then enter the Cart page three times, they’ll end up paying for 30 extra.
Also, I haven’t managed to make it so that only custom items receive the added fee, as non-customized items still end up costing extra. Can someone help me out?

You can use the new cart API - closeMiniCart feature immediately when item added

You have to check the item exists or not by getCurrentCart. If the item really not added, run the add custom item to vart

Can you please give me a more in-depth explanation? Thanks in advance!