Statement of research interest as an early Master's student
I would write about both. 

I usually think the writing of a statement of purpose as a story I want to tell. Write about your past projects to introduce you and your research interests, giving the reader some context on why you are applying for the position and the reasons your profile/know-how fits well in the job description. 

Even if you are not sure about the exactly subject of your next project, you must know the topics that are interesting for you and the ones you definitely are not willing to work ever. You are an early master's student, no one is expecting you to tell exactly to where your research will lead you. However, they expect you to give some clues in order to assign you with the appropriate supervisor and in a project that is best suitable for your ambitions.

I would suggest you to read this text where they summarise the main characteristics of a good statement of purpose.