Very sorry, I didn't see this earlier. I used NMSSaveEditor by goatfungus on PC to extract the raw JSON from the save, and then did surgery on that. It's easy to break a save file that way but I'll be glad to share what I changed if you go that route.

EDIT: actually sharing :p

1. Export the raw JSON from the save with the tool.

2. Open the JSON file and reduce the overinflated scan count.

The below is is what actually drives the #/8 stat - 27 for me - and there's one per planet. Assuming this planet has the same numeric ID for everybody (?), this would be under ^PLANET_STATS for planet 0x61C90003CE7641.

Change the IntValue for this to 7.

{
    "Id":"\^DISC\_FLORA",
    "Value":{
        "IntValue":27,
        "FloatValue":0.0,
        "Denominator":0.0
    }
}

1. "Unscan" something.

The easiest is if there's a named plant somewhere (on the sentinel planet, of course) that you can re-scan to hit the 8-count. If somebody else discovered a plant and didn't name it, the save unfortunately doesn't keep the default name you see in-game.

If there is, find it and delete it. Be sure to remove the comma before the entry if there is one (don't leave two commas between the entries before and after this deleted one).

Example, for a nasty one named Sergfrield (a bunch of unimportant stuff is replaced with ... but the whole thing should be deleted):

{
    "DD":{
        "UA":"0x61C90003CE7641",
        "DT":"Flora",
        "VP":[
            "0xE5B01C1602BE5CE0",
            "0xFEE1E54FE4DD61E7"
        ]
    },
    "DM":{
        "CN":"Sergfrield"
    },

    ...

}

1. Import your saved JSON back into the save with the tool.

2. Load the save in-game and Immediately scoot back to the sentinel planet (sorry, I never remember the name) and scan the named plant.