You are correct that the numbers I cited were off, because I had neglected to check specifically for numbers at the heliopause. Here is a better set of numbers:
The plasma density in the outer heliosphere is typically about 0.002 cm-3. The first electron density measured by the Voyager 2 plasma wave instrument in the interstellar medium, 0.039 cm-3 ± 15%, was on 30 January 2019 at a heliocentric radial distance of 119.7 au. The density jump, about a factor of 20, confirms that Voyager 2 crossed the heliopause.
In other words, the density of the interstellar medium just outside the heliopause, as detected by Voyager 2, was about 20 times larger than the density of the plasma just inside the heliopause.
I suspect you got your numbers reversed.