That's what the Build Array was there for... I think you may have made the job harder on yourself. The Array to Spreadsheet String will add in those commas between each element (each element in the row like you want) and then add line feeds after each row. Since there is an array being built within the For loop, you shouldn't need to put any commas there.
I know you already have it working, but for learning's sake you should post what your code looks like now just so we can help you improve.
