Oxford open offers

It means the opposite. Congratulations. If you meet any conditions attached to the offer, you will be given a place by a college, whether Magdalen or another. The university regards you as a candidate too good to miss.
Please don't worry about ranking yourself compared to others. You satisfied those who carefully assessed your application.

Hello, I have received an open offer underwritten by Magdelen college for Music, and I was wondering if anyone could tell what an open offer means in terms of how strong my application was? Does it mean my application was less strong compared to others for my first choice college?

Sorry, another question here! For the open offer, is there still any chance that i could end up at my first choice college or is that completely off the table?

You could end up there or at any other undergraduate college.
It is more likely than not that you will like whichever college you end up at.
One of my best friends was trumped* from St John's to Wadham. He tells me that he never missed being at John's.
*Colleges used to be able to poach a candidate from another college by offering an entrance Exhibition or Scholarship. This was called trumping. That system is no longer used.

Sorry there’s also one more question i have thought of! I was wondering whether as an open offer holder I get and offer holders day, as these seem to be college specific and I have not been told about one for me. I would really like to go and have a look around and get a feel for it however, so if I don’t have an offer holders day, do you have any other suggestions of what to do?