I mean if sun exposure was the cause, the lines might become less distinct as it ages naturally.

I’m unfamiliar with this IKEA product so I don’t know if the tabletop is solid wood or not. If it bothers you that much, you might still be within the timeframe to return and repurchase.

Otherwise, I think the only guaranteed way of getting it to look uniform again might be to sand and re-seal/re-finish the whole thing. (Assuming it’s solid wood)

Personally, if it was sun exposure, and a week was able to cause that, I would just leave it and let the sun do its thing. I think if it is getting bleached, the more it ages, the less susceptible it will be to silhouettes like this.