I had a theology teacher who told me that Adam and Eve were just myths, and that the rest of Genesis was all just legends. Is that what the Church teaches?

No. The Church has always taught that Adam and Eve were real people and were the first human beings from whom all other human beings are descended. In 1950, Pope Pius XII, in Paragraph 37 of an encyclical entitled Humani Generis, states, “…the faithful cannot embrace that opinion which maintains either that after Adam there existed on this earth true men who did not take their origin through natural generation from [Adam] as from the first parent of all, or that Adam represents a certain number of first parents.” In other words, the Church teaches that all humanity descended from Adam and Eve. They had to be real for that to happen. Paragraph #38 states: “This [encyclical], in fact, clearly points out that the first eleven chapters of Genesis…do nevertheless pertain to history in a true sense…” Again, Adam and Eve are not myths, and the rest of Genesis is not legend. They are history in a “true sense.”  
 
Paragraph #39: “Therefore, whatever of the popular narrations have been inserted into the Sacred Scriptures must in no way be considered on a par with myths or other such things…”  
 
And listen to what the Catechism says, Paragraph #375, “The Church…teaches that our first parents, Adam and Eve…” No mention of a myth here.  
 
Paragraph #404: “By yielding to the tempter, Adam and Eve committed a personal sin.” Myths cannot commit personal sins.  
 
Adam and Eve are not myths. Genesis does not contain myth or legend. That is Church teaching. If anyone says otherwise, ask him or her to produce sources from a magisterial document. They won’t be able to do so.