Are you sure that these are a contributions to a Roth IRA and not a contributions to a designated Roth account in a qualified retirement plan like a 401(k)? 401(k)s and similar plans are not IRAs. If the contributions are shown in box 12 of your W-2, these are not Roth IRA contributions. Any amounts shown in box 12 of your W-2 are to be entered only in box 12 of TurboTax's W-2 form, nowhere else in TurboTax.
Certainly the account value will vary from the amount contributed due to investment gains or losses.