Is W2 Box 6 supposed to equal the additional tax on medicare wages used by Turbo Tax to determine taxes already paid out of my income? The number in my W2 is higher

What?  Your employer entered the amount that you see in Box 6--that is how much the employer withheld from your pay for Medicare.  You just enter the data from the boxes of  your W-2 exactly as it appears.  What are you trying to do?

What number in your W-2 do you think is higher?  

https://www.forbes.com/sites/kellyphillipserb/2018/02/21/understanding-your-tax-forms-2018-form-w-2-wage-and-tax-statement/

Not sure what you are asking?   W2 box 6 is not for any additional amounts.  Box 6 for Medicare tax is a straight flat 1.45% of the amount in box 5.  No max.