It would have been helpful if you had indicated which plot you were buying!
As you reserved off plan, you have bought on the basis that the plot is as it was on the plans you were shown at the time you reserved.
If it is now different, you can pull out and all costs will and must be refunded to you.
Builders sometimes change plans because they have discovered a mistake, but they are required to tell you and give you the option to cancel.
As it is Persimmon Homes, my advice would be to cancel!
From your pictures, it looks like the garden boundaries to plots 69, 70 and 71 have been left off the plan.
Plot 70 will have the smallest garden anyway.
Persimmon can't even get this right!