MH152, what seems to be confusing about 300NM
(540KM if you fly in the continent),and last time i looked 298NM is less than 300NM I agree with BigGrecian, it is too expensive to start worrying about that difference, as CAA will ask you to redo the whole XC, and you will waste money and time
(I am assuming you are flying in UK/US if you are flying in an area where they are using KM then you should be ok)