Ang dating ng pregnancy ay trickier talaga, LMP vs ultrasound readings don't always match perfectly kasi ang dating scan sa early weeks (especially first trimester) ay mas accurate kaysa LMP, lalo na kung irregular ang cycles mo or hindi ka sure ng exact date ng last period. Since your first ultrasound says 33 weeks, that's likely closer to the truth, pero it's worth bringing this up sa OB mo sa next visit para i-confirm where you really are, baka may explanation siya kung bakit may discrepancy, or i-adjust niya based sa baby's measurements ngayon.