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.
"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 him (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."
But notwithstanding his resolve to improve, Bottas said 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.
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