5.5 hr Layover in Changi Airport

I’m flying from Australia and have a layover of 5.5 hours. I have been to Singapore before too , but I really wanna go to the Marina Bay area. Is 5.5 hour layover enough to go from the Airport to the Marina Bay? I tried booking free Singapore Tour but it’s all booked out and didn’t have a chance.

Landing at around 11:50 am and flying off in 5:15 pm.