I think that the first step would be to consider the main themes, ideas and/or issues explored in Sylvia Plath's poetry. Her poetry is characterised by themes such as nature, love, death, electra complex and psychic disorders. You should therefore examine the way in which those themes are explored in each of the poems that you will be referring to as part of your assessment task (which you may have already done as part of your analysis of Plath's poems) because understanding each of those themes well will likely assist you in adapting them into a narrative.
While I am not familiar with Plath's poetry, I think that if the objective is to highlight similarities and differences between the context of the poems and that of the present world, your narrative should explore the experience(s) of a character(s) in relation to one (or more) of the prominent themes. An example would be a character's own perception of love and the aspects of the present world that are consistent with their perception, as well as the elements that are contradictory and/or create a sense of shock in the character. Of course, you may wish to adjust this based on your own knowledge and understanding of Plath's poems as you see fit.
In terms of length, 700 words is neither a short nor a long word limit. Effectively addressing it would therefore require you not to write in-depth about aspects that are not very important to your narrative, such as introducing a character, and instead focus on developing and expressing the events of the narrative, which would require more words.
I hope this helps!