The Finn had a solid start to 2017 in retired Nico Rosberg's wake and was re-signed for 2018, but he slumped in the second half of the season.
"The season has been tough," Bottas admitted to The National, insisting that Mercedes were pushed hard by both Ferrari and Red Bull this year.
With his teammate Lewis Hamilton winning nine races and the title, Bottas admitted that his tally of two wins is not good enough.
"I was definitely hoping for more," he said, "but I am glad I have proven myself and the team signed me up again for next year.
"I couldn't beat [Hamilton] this year but I am working on my weaknesses.
"Next year's going to be the same thing. I need to again prove if I am going to stay with the team for a long time."
Notwithstanding his resolve to improve, Bottas said that he has always felt the support of the Mercedes team.
"I didn't have many issues with pressure as I felt the whole team was behind me," he said.
Bottas will go into the season-ending Abu Dhabi Grand Prix 22 points behind second-placed Sebastian Vettel.