That's not how side-chaining works...
You are mixing your bass and kick tracks together and then detecting normally off that mix signal. Probably not going to have much luck doing such a thing.
The idea behind side-chaining is to have the kick drum hits automatically turn down (duck) the bass track at those moments. You keep the tracks separate the entire time - there's no pre-mixing in this. You need to send the side-chain source audio to different track channels of your bass track than the ones used for the output. 1/2 are normally used for your stereo output. Send the kick to track channels 3/4. Set the detector input in ReaComp on that bass track to 3/4.
That kick signal needs to stay in it's own separate channel in the bass track to be useful for this and to keep it out of the actual mix audio.
Now, why anyone actually likes the technique of ducking a bass from a kick track might be a better question but you didn't ask that.
