Did Atlantis exist at one time?

The only "historical" records we have a place called Atlantis is a single reference to it by Plato in his work "Timaeus and Critias."  There is appears to be allegorical (not a real place) and that he is using it as a symbol of a nation that is overthrown by the gods because of its pride (hubris).  beyond that there is no historical evidence that should a place every existed.

I watched a video about it possibly being in Doggerland, I think it was by OverlySarcastic on youtube?

This is one of those imaginative stories told by a man who could write about it & nobody could read anyways so it just hung around as the writing of a movie and no one picking it up to produce it.

The Eye of the Saharah is claimed to be the city of Atlantis. You would have to watch the Youtube videos on this. They make a very good argument for this being Atlantis. 

It wasn't a volcano, just a major earthquake and tsunami in the Atlantic ocean off the coast of Portugal.

Hell yes, in fact it exists right now.  It's a casino resort on Paradise Island in the Bahamas.  

It may have existed at some time in the past.  It's most probable location would be the southwest coast of Spain since there has been so far, no evidence of its existence in the Mediterranean. Its sinking in a day and a night suggests an earthquake followed by a tsunami. 

That was what was known as the great flood.

Possibly.  During the last Ice Age, sea levels were much lower - possibly as much as 150m lower.  After the age ended, sea levels began to rise, and many lands that existed then were covered up.  Beringia, Doggerland, land to the west of India are just three examples that I know of.  Atlantis MAY have been such a place, possibly somewhere in, or near the Mediterranean Sea.

No evidence that it ever existed. Total mythology.