my fuel cap check light came on and i checked the fuel cap and it was on and tight and the light won't go off

 

If it was on correctly then your cap is faulty meaning it is'ent venting properly. You will need to purchase a new one and install. The light may take 4-6 start/warm up cycles to clear. You can always clear with a scanner or by diconnecting your negitive battery cable however I would not recommend the latter as your ecm will have to re learn all the parameters