The command you entered
sudo chmod u+w myfolder
grants write permission to the owner... There it is:
drw-r--r-- 13 myuser www-data
^--owner may write
You wanted execute permission
chmod u+x myfolder
(you won't need sudo if you own it). That will give you
drwxr--r-- 13 myuser www-data
^--owner may enter and search
(octal 744) - but there's not much point in that setting - probably you either want 755 (all can access) or 750 (owner and group can access) or 700 (only owner can access), since read permission for directories isn't much use without execute permission.