Google Cloud DNS – Subdomains wildcard not working

I got one domain example.com on app engine.
All subdomains a.example.com, b.example.com, c.example.com… have to point on example.com.

I'm configuring everything from Cloud DNS of Google Cloud, my configuration is like that:

*.example.com.  CNAME   300 ghs.googlehosted.com.
example.com.    AAAA    300 xxxx:xxxx:xxxx:xx::xx
example.com.    AAAA    300 xxxx:xxxx:xxxx:xx::xx
example.com.    AAAA    300 xxxx:xxxx:xxxx:xx::xx
example.com.    AAAA    300 xxxx:xxxx:xxxx:xx::xx
example.com.    A       300 xxx.xxx.xx.xx
example.com.    A       300 xxx.xxx.xx.xx
example.com.    A       300 xxx.xxx.xx.xx
example.com.    A       300 xxx.xxx.xx.xx

Already tried to do something like

*.example.com.  CNAME   300 example.com.

But not working.

If I use DIG to check my DNS, I got correct answer

;; ANSWER SECTION:
a.example.com.          300     IN      CNAME   ghs.googlehosted.com.
ghs.googlehosted.com.   218     IN      A       xxx.xxx.xxx.xxx

When I go on a.example.com from my browser, i got ERR_CONNECTION_CLOSED