Although my personal opinion is that assessment tests should be taken with a grain of salt, my experience with StrengthsFinder is that many people find it insightful, if not accurate.
Finding weaknesses in myself to improve is not a problem for me....emotional intelligence (the main weakness I want to work on).
With respect to StrengthsFinder, it sounds as though you may not have absorbed one of the key tenets of the program: fixing weaknesses can only lead to mediocrity, but building strengths can lead to greatness. That is, if you're not adept at a skill, working to improve in that area may get you to average, at best. On the other hand, if you apply effort to an area where you have talent, you're can reach above-average skill level (since you're not starting at square one).
I’m quiet, reserved, not good at thinking on my feet on a whiteboard — basically the opposite of what I thought people with this strength (ideation) would be. I'm better at staying on the periphery, analyzing the ideas written on a whiteboard, seeing connections, and helping the team move forward with a direction.
There's a bias towards extroverts in group situations (see, Quiet by Susan Cain, or her TED talk), but activity is not the same as action. Extroverts and introverts think and act differently; the buzz of brainstorming can spur the former, but it can leave the latter without "space to think."
Ideation isn't about whether you think best in a performative or an introspective environment - it's about the insights and concepts that you produce. Building the strength of Ideation doesn't mean you have to learn to "think on your feet." In fact, that might backfire if you're talking just to get discussion points, before your best ideas are developed. It does mean that you have to have the confidence and ability to get those ideas out of your thoughts and into the collective mind of your team. Un-shared ideas cannot be acted upon.
Consider the environment and culture at your workplace, and look for opportunities to contribute in your own way. If your team has a "whiteboard and go" approach to problem solving, how can you keep the conversation going if you have a great idea after the discussion ends? Not every meeting has to end with a decision, and having a reflection period before putting decisions into action can help. In fact, it's a good practice to leave the discussion open for people to contribute after the meeting has ended (especially important if your meetings tend to be dominated by a few good talkers).