@stevekennedyuk
Your screenshot does not show any dimensions?
Never mind - I found it.

What do you have General Precision set to in Preferences?

@stevekennedyuk
I am going to recommend that you take about 10 steps back and start over.
Create a new file.
1. Sketch one (and only one) line at a time anchored with one end at the Origin.
2. Immediately dimension the line.
3. What do you observe about the color of the line after dimensioning?
Now, repeat 1-3 for next line connected to either origin or previous line.
Now, repeat 1-3 for next line.
If at any time you see white dots or blue lines (or arcs) on your screen after dimensioning - STOP- and ask questions here before proceeding.
And make sure that you have Show Constraints enabled (as well as Dimensions).
