The 2007 world champion told Autosport: "I knew the gap was quite big still and we don't have that speed right now.
"Second is not too bad, it is the best I can gain with the team. I'd rather be in first place, but we didn't have the speed.
"The car works the way I want it to. It has been a pretty tricky weekend to get things exactly right, it's very sensitive, but we are happy to be where we are now."
Raikkonen won the season-opening Australian Grand Prix last month.