Three things:

1) Read other reports to see how it is commonly done - in the participant section.

2) You can simply report them as provided by participants (e.g., Female: N=9).

3) If you see results that reflect a pattern per a demographic variable simply state that your findings seem to covary with gender, for example (e.g., more women than men seemed to find social support valuable).

You are being pushed by your data into a mixed methods study; which is okay. There is no harm making your study mixed methods but more heavy on qualitative. If the quantitative data has value in your study, so be it. Use a pragramatic mixed method approach and move on! My view.

I have a different opinion on this. If a study is completely qualitative in nature in terms of data (interviews) collection, and the only quantitative data is simple demographics, which is almost always needed for all studies such as the N, then I still view it as qualitative and not mixed methods. I tend to see mixed methods more along the line of qualitative data (e.g., interviews) and also research questions aligned with the study purpose that use surveys and ask for answers by asking for a number response (1 to 5 for example), for example, that the researchers, in turn, then run some statistics on.

In published articles using qualitative data, it is relatively common to include a table of background characteristics, either in the Methods section or at the beginning of the Results. It usually is simply presented, rather than discussed in any detail.