Ah, least they're stuck inside Earths SOI rather than wanging around the solar system. How much were you off?
Actually I'm not being entirely accurate, I brought way more propellant than I needed (at least 63 tons extra, which was one additional tank), problem was my poor trajectory planning.
When the ship was preparing for a Neptune departure burn, it was unable to align the planetary alignment window with its burn window properly due to its highly elliptical shape, so I was forced to burn prematurely in order to secure a crude home trajectory before the window is completely lost.
With this crude trajectory, it required a very long inefficient correction burn after leaving Neptune's SOI, not to mention correction burns after being deflected by Jupiter's gravity due to an unintentional encounter.
This sapped the propellant till it was virtually running off fumes, like I could hardly see the indicator bar at all. But still it was enough to bring the ship's periapse to around 31km after the aerobrake.