Oh No! Wooden worktops are great as you can complete your own repairs. No need to panic! The area marked can be lightly sanded and then re-sealed with your treatment of choice. Any chance it could have been caused by water or iron pans being left on the surface? Hope this helps resolve the stain. Let us know how you get on. I have had the same happen to me many of times
do you have any heavy cast iron pans or casserole dishes as I know these can cause stains on wooden work tops? I have metal trivets that I use to put hot things on but I think even cold iron pans, if wet, can cause markets. Just do as above - or be a slob like me and relish the well used look of your worktops in due course!