When inserting a new note the pitch of the new note should be the same as a pitch of the previously inserted note. Or C-3 if it's the first note.

Here's what happens if you do right-up-left on a pattern screen. Shouldn't move cursor two times up.

When song or pattern is not playing adding a note should play this note

Do not loop the whole song, check the next row and if there are no patterns – move to the first row. Even better to find the first row in the current consecutive sequence of rows with nonempty patterns.