Many thanks for all your input.
I was using just a piece of pine that I found in hubbys shed. I was using a No3 reverse blade, I'm pretty certain my table is square because my 'letters' fall out perfectly.
I don't have a photo as I threw the piece onto the fire, literally But it was exactly the same problem I had when I tried thicker flat wood, the 'backside' was nowhere near the shape of the pattern that I'd cut on the front. I tried not to 'push' but perhaps I did without thinking.
Where I cut on the front of the pattern looked perfect but when I looked at the 'backside' the cut was miniscule. If I had to describe what I saw, then I would say a 'V' shape. I may try using a piece of 'proper' wood and a different blade next time. But I'm easily discouraged and don't feel like trying again just yet.
¼" plywood (which I use mostly) is such a forgiving wood that I don't have a problem cutting that.
I have an Axminster Trade Series saw which performs beautifully on anything else I cut.