Should i buy some smaller sizes.....?

i had a growth scan yesterday as my baby was measuring small for dates at my anomaly scan, she is growing well but still slightly small. my daughter was 8lb 1oz which was big for me, newborn sized clothes were still quite big on her though so should i buy some smaller baby sized clothes for this one just incase? what are the chances she will catch up and be born a good size similar or bigger than my daughter was? was anyone told they were having a small baby but they were born an average or bigger sized baby? my bump is measuring correct for dates, she moves alot and doesnt feel small to me, is there a chance their measurements are wrong or are they always accurate from a scan? thanks.