In most cases exercise will lower your Bg levels, which may show up several hours after exercising. So, the increase you had might have dropped later.
However, it can also have the opposite effect........raising Bg levels. This sometimes happens when Bg levels are high prior to exercise. It can also happen if you do some very strenuous activity, this can stimulate your liver to 'dump' extra glucose into your bloodstream due to the increase in Adrenaline in your body.
So depending on what you are doing exercise can make Bg levels go up.....or down. It is a balancing act really which by testing at various times you will see what effect different levels of activity have on YOUR body and Bg levels.
Ken