Oh ok, youll be completely fine. Fitchburg is a larger town than natick and its downtown is much larger and more dense. What part of natick are you going to, the mall I would assume? Natick has a small downtown and is more spread out if thats where youre going its not bad at all. If youre going to the mall its not near downtown and instead is across the lake and essentially in framingham. If youre going there its literally right next to rt9. You can avoid the pike entirely and just go 495 to rt9 and then the mall will be on your left.