How about a similar situation.
You're asked to pick an Ace of Hearts from a pack of 52 cards, face down, so you have no way of knowing, which it is, but the dealer does.
You choose a card, leaving it face down, so you don't know if you're correct or not.
You must agree that the chances of you choosing the right card, from the 52, is highly remote.
Now the dealer reveals 50 of the remaining cards, leaving just the two face down. The dealer knows which is the Ace of Hearts.
Are you better sticking with your original choice, or swapping to the other card?
The original odds remain, 1 in 52 of choosing the right card, it's just that you now know the other 50 are not the Ace of Hearts.
If you had been originally presented with a choice from 2 cards, it would be 50/50. You weren't, it was a choice from 52.