How can an animal even have a neck that long? Was it clear from the fossils that it is this long because I am skeptical.

This video [0] tries to answer the question of how we know what we know for a different species but I imagine the methods are similar.

[0] https://www.youtube.com/watch?v=5vea06e6x_E

relevant xkcd: https://xkcd.com/3185/

No, there's no way to tell—the paleontologists probably just took a bunch of bones from the site and threw them together in a way that looked cool. /s