Scan not complete

Lindsay • 30 years old,2 daughters 11 and 10 to a previous! 1 AngelBaby baby #3 after ttc 4 years! Love my Liam lots xxxx
Been for my anomaly scan today at 18 weeks  4 days and have to go back in a week because they couldn't get good enough views of the heart or spine. They told me not to worry as what they did see looks normal but I can't help but worry! Anybody else had to have their 20 week scan in two parts? Thanks in advance xx