Sometimes when you are using carpenters glue between strips, you will end up with white glue lines. These lines are typically due to the glue being too cold as it dried.
One way to make the lines disappear is to heat them up with a hot iron. This heats up the glue enough to melt it slightly. When it cools off it becomes clear.
You could probably use a heat gun as well, but it will heat up a larger area and you may soften the glue to the point that the seams pop. That would not be good.