Do airlines ever downgrade first class passengers to economy?

I have never flown first class before. Always wanted to at least give it a try. Back in April of this year, I booked my flight to see friends over the holidays in December. Back in April, the first class seats were being sold for only about $150 more than economy seats. So I booked first class.

Now that my flight is only about 3 weeks away, I was curious as to how much the first class tickets were. Delta says there are 3 first class seats available for $1500 each. But when I click on the seat map, all of the first class seats are taken.
I don't have any special status with Delta. Will I be downgraded back to economy? Is there any compensation if I'm?
I've been looking forward to experiencing this flight for months just to cross it off my bucket list. I would hate to be sent to the back of the plane, especially after paying extra to sit up front.

Added (1). Maybe I wasn't clear, but there are 12 first class seats on this A319 aircraft. All 12 seats are taken… And they are still selling 3 more seats. How can they sell 15 seats if only 12 seats exist?

I'm CONFUSED. Asiana Airlines Baggage?

So, me, my two brother and my dad are going to have vacation in Korea next week. So there are 4 passenger in total. We're allowed to carry 2 luggage (23 kilos each) and a hand-carry(10kilos).

My question is does EACH passenger can have 2 luggage+handcarry? Or 2 luggage+handcaryy is for ALL of us?

How can I cancel my flight on copa airline?

On Day before yesterday I booked a flight ticket on Copa Airlines but now I want to cancel my flight reason being for some personal reason I can't board the flight, so can any one help me for the flight cancellations of Copa Airlines. How can I cancel my flight on copa airline