This is a very hard one to answer as I am pretty sure there would be more general rules stated elsewhere in the schedule you filled and quite possibly as option Z clauses.
On it's own though, be aware of clause 52.1 second sentence which states "Defined Cost includes only amounts using RATES and percentages stated in the Contract Data and OTHER amounts at open market or competitively tendered prices with all discounts, rebates and taxes deducted."
So if the rates are stated as part of your tender in or referenced from the Contract Data, you could argue, given 52.1, it doesn't matter what they actually are, it's what you tendered and the Employer accepted. However, I can see their perspective and as, I said, I would be surprised if there weren't other words elsewhere which impact on the interpretation.
The complication, as you point out, is the words "Not to be exceeded ('ceiling') Rates & Fee Percentages". A literal interpretation would be they won't be exceeded but they won't be less 'cos that's the figure we tendered and you have accepted.