First off, double check to make sure you have correctly assembled the heli, not saying you have not but some of the instructions that come with these helis are not the best in the world.
If you built the 450 properly (ball ends in correct spots on servo horns, correct linkage lengths etc) and know for sure your swash was level, It sounds like a servo or two may need to be reversed.
Make sure you have your radio switched so the motor is off turn on the radio and make sure heli is powered and check as follows.
Push the throttle up slowly, swash should remain level as it raises as you raise the throttle, basically the three servos that attach to the swash should all push up on the swash plate.
If one or more are pushing down, reverse those servos on your radio so they push up.
If they all push up but not at the same rate, you will need to check and adjust end points on servos that are not throwing properly.

Every setup is different so make adjustments according to your heli, someone elses settings for the same set up can be a good starting point, but in no way guarantee they will work right for you.