Mercedes has presented a major aerodynamic update for the start of this week's second test, after the quiet start of preparations for Barcelona last week.
Although Bottas is confident that the renovated wing and nose have overcome some handling issues that have tainted the first try, he thinks the team is not yet in a position where she can be confident of matching Ferrari.
"It's better, but if that's enough, that's the big question mark," the Finn explained. "I have seen a lot of improvements since last week thanks to the stability of the car and the overall support of the car.
"But we really think we have not unlocked everything there is to unlock.
"We still need to make improvements, but at least we still have time after the tests to learn more for Australia."
Although Ferrari had a setback for its test program this week when a rim problem caused a big crash for Sebastian Vettel, the Italian team continued to impress with his pace.
Bottas said his opinion last week that Ferrari was in the lead had not changed.
"They always seem strong, obviously, as has always been the case at the Melbourne trials, a lot can change, but the package is solid.
"I still think we need to release more of the new package so we can really compete with them."
After revealing that Mercedes' main problem from the first week was finding a consistent balance for a full lap, Bottas said progress had been made on that front with the new aerodynamic update.
"From last week to last week, we certainly have been able to improve the overall balance of the car and the balance differences we had with the speed range," he said.
"We have been able to improve grip, support and stability overall, but in all these areas we can always do better.
"This is not yet the ideal car.We think the potential is there.It may be another car that has quite a low potential, but once you take it, it is can be very fast.
"We are learning massively every day, I think it's a good step back, and every time I get back in the car, things improve." I hope to feel it again this afternoon. and tomorrow and, hopefully, for a bigger step in Melbourne. "