Your sight range should not drop (other than a temporary spell effect). With Elven Sight at level 3, your range should be twice that compared to the start of the game (if you recall clearing the fog of war around Aleroth).
The base sight range for a new character is 12. The levels of Elven Sight add an additional 2, 4, 8, 10 and 12 to the sight range. Assuming no other sight bonuses, removing the amulet to drop from level 4 (36 total sight range) to level 3 (26 total) should be almost a 28% reduction (so roughly a 1/3 drop).
A reduction of 2/3 when you remove the amulet (drop of 10 sight range) implies your sight range is 5 when the amulet is off. It should be 26 (neglecting other sight bonuses), so you could learn levels 4 and 5 of Elven Sight (if you are at a high enough the character level), save, and then use the editor to unlearn a couple levels (so you are not using your skill points to fix a game glitch). Alternately, you could unlearn the 3 levels you have, load the game, re-learn up to level 3, save, unlearn, load and re-learn level 2 (or just keep going until you get the sight range back to normal).
