I'm going ro leave the plane, but wearing the parachute does not give me points. It should give me 4. After landing on Nontoonyt Island and cutting the ropes I should have 350, not 346 points.

Are you using a walkthrough for points? Maybe it is incorrect, look at this ;) - http://www.sierrahelp.com/Misc/PointLists/LSL2Points.html

I'm using this one - http://www.gamefaqs.com/pc/565081-leisure-suit-larry-goes-looking-for-love-in/faqs/23172 - it has at least one mistake (swapped lifeboat and pool on the map), but unlike the Sierra Help one, it has all 500 points. BTW, I tried playing the game in DosBox instead of ScummVM and this time I've got the points. Maybe it's a ScummVM issue? Now Ii'm trying to pass the quicksand on Nontoonyt Island, but without luck.