No, let it go- mgood4u - let it have time to get established. Next year it will fill in more. Hope you gave it plenty of room. Left to grow to it's natural shape is best.
Forsythias should never be sheared. When it becomes a bit large in years to come, prune by removing older canes, cut them to the ground.

I have five enormous forsythia that are four years old and I just pruned them for the first time last week! They line my sidewalk between the walk and the porch and had gotten so big that I had maybe 6 inches of space to walk on the sidewalk. They're all about 7-8 feet tall (my porch sits on stilts 8 feet up)so I just trimmed the sides that were taking over the sidewalk. This past spring they were just beautiful...covered top to bottom in blossoms. I would just let it go if it's not in the way of anything. I know that if you wait too long to cut them you'll cut off all of next spring's blooms.

Always prune your forsythia directly after blooming in the spring. Don't worry, they are hardy things. I have some I want out, but they just keep coming back like a bad penny, so I guess I'll just have to control them where they are. Another example of how tough they are, I had put some rooted branches in trash bags cause a family member wanted them, well they never came and got them, so they sat in those trash bags over a year, no watering nothing, a friend of my said she would take them when i said I was heaving them on the brush pile to burn, they are growing wonderfully. Ann