Develop module inadvertant Perspective scale woe

[Hypnoswan]

Lightroom Version Number

6.14

Operating System

1. macOS 10.13 High Sierra

I had pressed 'L' key a few times to inspect the image an in the process managed to also click on something else which produced the attached result. (a huge border!) I discovered from 'history' that it is called 'perspective scale' but where do I find it and how do I undo it? ( I realise I could create a virtual copy and reset the RAW image but Im curious)

 

[Johan Elzenga]

In the Transform block, you apparently set scale to 50%.

 

[Hypnoswan]

yes ! that's it! thank you

how on earth I did that is still a mystery