Bump and movements help

First time pregnant , currently 20 weeks , normal scan at 19 weeks ,still not very prominent bump (just a small full belly that only i notice) ,its not not noticeable to others yet , feel some occasional flutters for a moment in between few days ,no regular moments / actual kicks ..is this normal? Also ,is it ok to measure a week behind on 20 weeks scan? My scan was at 19+4 d and baby measured 18+5 days (all parts measured different)