Used Nix (permethrin) lice spray on couch and chair. So nervous it is going to cause cancer in my toddler is the risk really bad? Used it in August. I'm panicked.

No Do not worry. Chemicals like this do not cause cancer that easily. First of all anything that carries much risk for Cancer will not be available for use. Further, it takes many years of repeated use and exposure before Cancer can be created. Our bodies are very efficient in cleaning up any chemicals that enter our body. Even if some cell damage is done , the body can repair it quite efficiently.
Nix (permethrin) and toddler. Not an issue the main ingredient in Nix (permethrin) is derived from the flower chrysanthemum and is a common ingredient in a lot of household bug sprays. As long as it dries before they come in contact with it - its NOT a problem. To eliminate lice in furniture - you might want to wrap it in a big tarp (like a tent) and use a bug "bomb" aerosol spray. just air it out afterwards Good luck.