Press the PAUSE button || (bottom-left) to momentarily stop recording. Press it again to resume.
To make a fix, slide the bar to the cut point, then hold down the left mouse button while parked on the cursor and swipe right, to make a selection.
Press DEL on the keyboard. The selection is deleted.
Press the RECORD button to resume from that point.
Made a mistake? Press <ctrl-Z> (or Edit | Undo) to go back, step-by-step.