I think you're getting the song editor confused with the piano roll. Just right-click any of the squares on the track you want to open and a box of options should pop up next to your cursor. Click "Open in piano-roll", and then it should pop up.
And also, you're not going to be able to stretch your notes that you placed using the b&b editor, so just make new ones in their place if that's what you want to do. If you want to raise the percussion note up or down a few notes, then you can just click and drag the note you made in the b&b editor to where you want it.
If you want to move the notes and instrument entirely from the b&b editor and put them in the song-editor (which is what you could be talking about and I'm totally wrong on my assumption that you're getting the song editor and piano roll mixed up) right-click the percussion notes, select copy and then paste it into the song-editor onto your instrument.
If you made this instrument yourself and you don't have it in your folder of presets then just save the instrument, click the refresh button next to the search bar underneath all the presets, open the folder where you saved it and then drag it into the song editor. Then you can paste your notes onto the instrument.
I can provide images if you don't understand this.
