ACan I add lemon extract to lemon curd? My curd taste more eggy than lemony.

AI don't know the answer to your question.

I will say my absolute favorite recipe is the one from Cooks illustrated..

To me, lemon extract tends to taste bitter.  I would recommend lemon oil if anything.  I think that you might just  need  a better recipe.  I love the one from The cake bible.  it is tangy, and very clean, fresh and lemony. Just egg yolks, lemon juice, sugar, butter and zest.  When the curd approaches 190 degrees I cook it at that temperature for another 5 to 10 minutes, stirring constantly to make it extra thick.  It is just wonderful as a cake filling, and also  mixes beautifully with buttercream. (It also freezes well).  HTH

http://www.tastebook.com/recipes/514932-Lemon-curd?full_recipe=true