I can not duplicate any issue with day2 temp displays... all sizes, at all DPI, show both numbers in Celsius and Imperial.
I remember there was an issue with 2nd day temps, but it was a typo showing wrong temp, nothing concerning display.
I would recommend downloading the package again ('Download' button above right) and re-install and see if that cures your 2nd day issue.
If that doesn't work, let me know that, also include your display resolution, Rainmeter version, Windows version, and anything else you think may be affecting your display.
As I said, I do not have any issues, and no one else has reported an issue.