As long as the drivetrain seems to work, I'd probably be more concerned about the security of the retainer cup on the non-drive side than an off-center spindle. In the days when 3-piece cranksets were standard, asymmetric spindles were fairly normal, and often deliberate to minimize q-factor (although this typically involved making the drive-side longer than the non-drive side, whereas the OP is doing the opposite).

If the chainline is problematic, it's possible that a 2.5mm spacer would "correct" the situation. Although given that the OP just shoved a 73mm bracket into a 68mm frame, I'd want to know more details before assuming that the spindle length is "correct" for the drivetrain in the first place.