I'm guessing the lavender is pushing out new shoots at the front of the plant, so they look like they're going sideways. As the plant continues to grow, newer growth will grow straight up. If it doesn't "get straight", you can always prune it back; lavender's tough and can take a lot of pruning.

Jim

I had the same problem. My plant is not even a year old but the stems which are more than 15" long were growing horizontally. I cut them down since they were smothering my chives so now I only have a couple of shoots that are a couple of inches high.
Since lavender don't flower the first year I guess I now have to wait even longer for them.
I grew my plant from seed and it's in a south/southwest location so it has plenty of sun all day. I wish I knew how to get it to grow upright.