Trying to add an arbitrary amount of 'time' to a datetime value which starts out containing ONLY a date is fraught with problems. Try adding the last millisecond or two, for example. The way that is ALWAYS safe is to use >= @YourStartDate and < DATEADD(DAY, 1, @YourEndDate) as your range.

My apologies for not noticing my typographical error, before posting. Of *course* the comparison to the DATEADD(...) should only be less than.