Hi,

The dimensions you are talking about are taken from top view. What is the
rate at which you are electroplating? Possibility is that, if you over plate
beyond the dimensions of the thickness of the resist, the gold grow out on
both sides and that could be one of the reasons you read 49 um.

One other reason could be the side wall of resist. If it a positive resist
you are using, the regions developed (where you are going to electroplate)
will be wider on the top and narrower at the bottom. SEM is a good way to
find out what is happening.

krishna