After reading this I might recommend not to fix it. It looks great and its not broke lol. Maybe just wait and see how things pan out. If it does happen to split, you know the issue. If it doesn't then 🤷‍♂️

Hi there. Looks great however there will be some tricks and repairs you may need to make come end of winter. As the winter thaws and the air gets humid during springtime, the wood expands and contracts. The apparent expansion and contraction you will see is very apparent in the direction parallel to the grain of wood. It is not so apparent perpendicular to the grain of wood. Basically wood planks are like grown adult men, They cant get taller but they can get wider. What you'll see in springtime is some board splitting because the boards are spaced too closely together and have very little gap between planks. since they cant expand to get wider, the planks start fighting with each other until they fail at the fixture points (where the screws are) You can see the apparent spacing on the older fence that is in the top right of the image. Spacing the planks apart is by design and not poor worksmanship. Hope this helps you in the future but otherwise looks great. Never stop DIYing :)