Ok, the seam is perfectly fine. I'm not sure where you got the 2mm figure from, but it looks like less than 0.1mm (if any) offset between the rim-ends. Here's what I recommend.
1. remove tyre and clean off all glue
2. true wheel radially and laterally to +/- 0.2mm (0.1mm trueness is available from a lot of wheel-vendors)
3. use calipers and measure the rim-width
all the way around. Easiest to clamp it around one spot, then slide the caliper around the rim and feel for sticking points.
4. use a file on the high sides of this seam:
It really doesn't look that bad. It appears to be a criss-cross type of misalignment, so you'll have to file the upper 1/2 of one side and the lower 1/2 of the other side. Then file both in unison to get a perfectly flat surface. Then finish off with fine-grit sandpaper moving along the direction of rotation to blend it all together.