Practice stroke hits the ball - what ruling

[Liverbirdie]

I was playing a bounce game with my mate and whilst playing a practice stroke on the putting green, I knocked my ball 8-10 inches to my right.

He'd got a birdie 2, it was my second shot. I replaced my ball where it was, as I thought, it wasn't a genuine stroke at the ball - was I right? I then followed him in for birdie, but I still give him the hole (in case). Luckily I still beat him 4/2.

What should I have done, played 3 from where the ball finished, or replaced it and taken it from there, without losing a stroke?

 

[Whereditgo]

Rule 18 - 2 I'm afraid

Penalty of 1 stroke and replace the ball

 

[Liverbirdie]

Rule 18 - 2 I'm afraid

Penalty of 1 stroke and replace the ball

Thanks, I was looking in the rule book coming down the next hole, but wasn't sure which rule came into effect. I'll check it again.