IL, Try this next time: look on ebay for prices realized ONLY. Then look up the book on bookfinder.com . That should tell you if what you have is the same as what sold on ebay. An edition is a set of plates. A first edition can be printed/reprinted for 20 years -- unlike what most people think. What you really want is the first PRINTING or first STATE of a book. Simply, a printing is a chunk of books which were printed at the same time, without corrections or changes to the text.
And, to help you not feel so bad? Books are ground up trees and rocks mostly. They almost never have intrinsic value, not having gold, jewels, etc. used in them anymore. A book is worth what someone will pay for it because of that. It's all supply and demand. Yes, you probably could have gotten more, maybe a lot more, but you also could have held onto the book trying to sell it for that for years. ( I have a storage unit full of such volumes.)