I see 3 options.

1, adjust your z-offset. I’m not familiar with prusa’s firmware, but if your first layer is bulging, it could mean your z-offset needs again.

2, see if your first layer line thickness is set above 100%. By default some slicers lay an extra thick first layer; you might try decreasing this.

3, get rid of the white on the first layer, and just make the second layer white. This is how I do multi-color lettering/ designs and it works incredibly well. I can show you pictures if my description doesn’t make sense.