Marble Madness is tough, probably to make up for it also being kinda short, so you're going to be running out of time frequently, until you've mastered the game... which might take some time.

In the meantime you could start up a two-player game (even though you're only going to be playing single player)

Then race normally, letting Player 2 just sit there for a little bit

As you race to the finish line, the second player will be scrolled off the screen, and brought back closer to where you are, incurring a 5 second penalty each time. But if you can get it across the finish line before its time runs out (which should be totally doable on the first race), whichever marble crossed the line first will get a five-second bonus at the beginning of the next race

Which doesn't sound like much, but trust me, you're going to need all the help you can get.