Half my early mock mistakes weren't about not knowing AWS services, they were about confusing which service fits which use case. EC2 vs Lambda, S3 vs EBS vs EFS, RDS vs DynamoDB, the exam loves scenario questions where picking the "almost right" service is the wrong answer.
Fixed it by drilling comparison-style scenarios on CertBoosters until the use-case boundaries actually stuck instead of just memorizing service names. If you know what each service does but freeze when asked "which one fits this situation," that's the gap to close before exam day.