Bobbin thread issue on new machine

Question

I have a brand new Brother ns-10. I have threaded upper thread correctly (tried about 12 times) and redone the bobbin 100 times more. When i am sewing a straight stitch the top stitch is perfect but the bottom (bobbin thread) is almost a zigzag stitch rather than straight. I have adjusted all tensions but to no avail. I was hemming up soft denim jeans using the correct thread and a 90/14 schmetz brand needle which is brand new. Can anyone suggest what the problem might be. This is a machine that i have had for 5 days and i cant get the thing to sew right.