@Bria On the track header there is an option you can turn off.
There's also an option in Preferences. Double clicking the end of an event makes this happen, personally I have this on as i find it a useful tool but I can see how it can be annoying.
item 28. Why is my video track split between "A" & "B" tracks? If a red square bracket appears at the end of one of your video events then you are in Expanded Edit Mode. To exit expanded edit mode, do one of the following:
If no red square bracket appears then your track layers are simply expanded. To "unexpand" them, right click on the track header (the area to the left of the track) > uncheck "Expand Track Layers".