My paws fit but me head gets stuck!

So there's this little rectangular slot in me front door...

I watch envelopes and things get pushed through some mornings..and I didn't understand how it worked..

But then mum showed me its a little door to outside!

So nows I can stand on me back legs and and open it with me front paws and push me face under the little flap, but I can't go no farther! Me head keeps getting stuck. It's a bloody tease! I can feel the cool, fresh breeze on me paws and smell it with my little nose but can't get through the slot! I even tried using me back paws to climb up and force me head through the slot but me heads just too big!

I just want to go outside :( though I have managed to sneak past dad twice in two days..