It looks like you worked really hard securing the sandwich with pins. I find you just can’t get the backing smooth enough with pins or thread for machine quilting. I either spray baste or use Hobbs 80/20 fusible batt. If you still want to proceed, I suggest rather than doing long straight lines( the backing is going to pucker) try doing separate motifs. Do 5 inch lines spaced all down the sandwich and then turn the sandwich and make them into X . With them being separated, it will allow the extra backing fabric to puff between the X’s .