121.5 is your friend.
Do not be afraid or ashamed to use it.
I did once,shortly after I qualified.
I took off into fading light (I got chatting for too long at the departure airfield) and my 12 minute hop from Elstree to Denham ended up with me in the Heathrow TMA in darkness and calling up 121.5.
I'd had the sense to turn North as soon as I realised I was lost and then sought help which was duly given without fuss. The only slight drama once they directed me back to Denham was that this was my first night landing!!