Not sure what exactly you mean about the collecting and analysing of data part?
Methods for collecting / gathering primary data include things like interviews, questionnaires, and surveys.
Methods for analysing that data include things like thematic analysis, discourse analysis.
So what methodological techniques are you going to use when you examine the data that comes back from your questionnaire?
My supervisor suggested saying its a mixed method survey instead of research?
I don't understand this point. You are undertaking research using the survey technique. perhaps its the use of the "mixed method" that is problematic. If you are only using the survey, then is that perhaps a single method?
Maybe you should do a bit more reading into surveys as a research method in those methodology books - it might help you straighten things out in your head.