I'm able to create scratch org which I can see in my trail dev hub but I can't open them.   from "Get Ready to Create an App" tailhead
 
pogilvie:~/Projects/geolocation-> sfdx force:org:create -s -f config/project-scratch-def.json -a GeoAppScratch
pogilvie:~/Projects/geolocation-> sfdx force:org:open
ERROR running force:org:open:  No defaultusername org found. 

I've also tried:

sfdx force:org:create --setdefaultusername -f config/project-scratch-def.json

and I get the same error.   I wished I tried this out yesturday when I was a trailhead dx!    
 

I'm able to create scratch org which I can see in my trail dev hub but I can't open them.   from "Get Ready to Create an App" tailhead
 
pogilvie:~/Projects/geolocation-> sfdx force:org:create -s -f config/project-scratch-def.json -a GeoAppScratch
pogilvie:~/Projects/geolocation-> sfdx force:org:open
ERROR running force:org:open:  No defaultusername org found. 

I've also tried:

sfdx force:org:create --setdefaultusername -f config/project-scratch-def.json

and I get the same error.   I wished I tried this out yesturday when I was a trailhead dx!    
 

If something goes wrong in lightning component and I go back to component bundle and mofidy the logic there and save and comeback to browser and refresh the page and execute the component , But the component is sometimes displaying the same old logic. Is it because the Javascript handler code is being cached in browser or any other reason. I am able to look at the new logic in browser after making three or four refreshes.

I cannot for the life of me, figure out what could be wrong with my campingList component markup for the "Create a Simple Camping List Lightning Component" challenge.  This is the markup for campingList.cmp:

<aura:component>
     <ul>
        <li>Bug Spray</li>
        <li>Bear Repellant</li>
        <li>Goat Food</li>
    </ul>
 </aura:component>

Please help me figure out why I am getting the error.  Thank you, Susan