The "maximized contribution" button is simply a tool to help calculate what your maximum contribution limit is given the information you have already entered into the program. Generally, it would be used by someone who hasn't yet contributed to their plan when doing their taxes and wants to know what the maximum amount they can contribute is - so, they can check that box and then TurboTax will run a calculation and tell them a contribution amount. Then, they can contribute that amount by their plans due date.
One thing to watch though - if you check the maximize box, TurboTax is going to assume that you are going to contribute that amount by the due date and it will place that amount on Line 28 as a deduction. So, you only want to check the maximize box if you are going to, in fact, contribute the maximum amount. Otherwise, you should just enter your contribution by typing it into the program.
Since you have already contributed to your plan and figured out the maximum on your own, you would not need to check that box and you should just enter your contribution by typing it in.
