I replaced a timing chain and one side is seems to be loose how can I fix it?

I'm not Familiar with the ford in specific however MOST engines Do have a loose and a tight side the loose side generally has a nylon "tensioner" that presses against the chain keeping it snug. This is to prevent the chain from snapping, when throttle is suddenly applied, This generally not used on the stronger double roller chains, but I have seen them used with these as well. The tensioner is usually part of the timing cover but not always. Not knowing which engine you have I cant check to see if your engine uses a tensioner and if so what type and where it is located.

I would check to see if you have your tensioner on correctly and all the marks lined up correctly. Thats usually the problem.

Hope this helps Mike

Easiest first, double check you have the right timing chain. Are there guides or followers that may be worn, or out of adjustment.