If you had used Copy and Match Style in the first place your note would have had a coherent style. But in that case you would have lost any formatting like italics as Copy and Match Style inserts only plain text.
The Script menu has a number of options like Body Normal under Format. The editor pane’s context menu has Font/Styles… and CMD+t launches macOS’ own font picker. All of these options allow to apply one font style, so again italics and such would be gone if you went for a regular font.
So Markdown isn’t the worst choice to make.