Yours is a common problem. Your teacher wants an interpretation and you give a plot summary.
What your teacher is looking for is a comment on the effect of this scene on an audience. What makes it work as drama? In order to do this, you have to shift your thinking some.
Stop thinking of the play as a book and start thinking of it as something you can see, something that can affect your emotions.
Think of a film...say...300. If someone asked you what was so good about the movie, chances are you wouldn't tell them every single thing that happened in the movie from start to finish. Instead, you'd talk about what you saw and felt. Maybe you'd describe the graphic visual images or maybe you'd talk about the tension and suspense that built up--and you'd give some examples of how that happens. Maybe you'd talk about the exchanges between the two sides and the effect they had on the audience. How did the director build sympathy for the underdogs?
OK. Now...a play is the same thing as a screen play. You need a director to come along and decide on the lighting, the nuances in tone or voice or expression a character will use, and even the blocking (where people stand) on the stage.
A screen play has all of the bones of the movie already in place. Your job is to analyze the potential effects of these bones on an audience.
In this scene, there is tension:
Romeo walks into his enemy's house disguised by nothing but a little mask. Juliet walks into the party after having an incredibly disturbing conversation with her mother. Tybalt walks about looking for trouble.
There are potential complications:Paris watches Juliet and some suggest that Juliet's mom, in turn, watches Paris.
There is romance:
When Romeo and Juliet first meet, there is much play and bantering.
Think back to 300 or to some other movie that moved you, and try to identify the parts of the film that caught your interest and hooked your emotions. All you have to do now is to think of the parts of that scene that have the potential to interest and affect an audience and describe the effect that each of these parts might have.
If you described what happens, you would just summarize the events. You'd say, for example, first the servants enter, then they leave, then Lord Capulet and the guests enter.
That's just a summary.
To explain how this scene is an effective piece of drama, you need to ask yourself one question: what does it mean for a piece of drama to be effective?
For example, imagine someone said, "What makes that a great deal on a car?" You'd focus on the things that made a great deal great. You'd say, "It is a great deal because of the low price, low miles, and powerful engine" (for example).
In drama, you'd say, "To be effective, a piece of drama has to do ---" (and you'd fill in the blanks with all the important qualities. For me, one of the those qualities would be entertainment. I could then say, "One reason Act I, scene 5 is effective drama is because it is entertaining when Lord Capulet enters making all those bad jokes about the women dancing with him."
You'd then go through each major quality you see as part of effective drama and find something in this scene to explain as an example of it.