Side A and Side B of the cassette are recording on top of each other. How do I fix this?
If you mean you have two independent stereo shows one above the other, yes, that’s what happens when you press Stop between recordings.
The easiest way out from here is use the Time Shift Tool (two sideways black arrows) to push the bottom track sideways so its beginning happens after the top track ends. Attached.
Audacity will push the two together into one single show when you Export.
You can prevent this in future by record pause (P) instead of Stop between the two sections of the show, or do actually Stop, but Append-Record (Shift-R) to get it going again.