Hello,
 I follow the instruction and enable Dev Hub but I am still getting error 
 sfdx force:org:create -f config/project-scratch-def.json -a HelloWorldLightningWebComponent
You do not have access to the [ScratchOrgInfo] object
sfdx force:org:list --all
=== Orgs
     ALIAS   USERNAME                ORG ID              CONNECTED STATUS
───  ──────  ──────────────────────  ──────────────────  ────────────────
(D)  DevHub  dannyxxxxxx@.com           00Df4000004miAiEAI  Connected