I was moving a switch to a ceiling like and I used 12/2. when I finished I realized that all the wiring for the lights was done with 14/2. is it OK?

As long as the breaker is a 15 amp it is OK. A lot of electricians run a 12AWG to a junction box and then 14 AWG from that. Use a 15 Amp breaker with the 12 AWG and you help reduce voltage drop.

Thanks a ton