The Bees would have moved above Rovers into second, safe in the knowledge they only needed to avoid defeat on the final day, had they beaten Hartlepool at the weekend.
But they could only manage a 1-1 draw meaning it is win or bust at Griffin Park in four days' time.
"Doncaster have been up there all year," said Rosler.
"They were relegated from the Championship last year and have a higher budget than us.
"We are the challengers. We are in a great position. I like that for my players. We are better when we have to attack and win. On our home pitch we can definitely do that."