You can't remove a material you've added. Work in small quantities, or with diluted materials, to avoid waste.
Joining one or all of the Yahoo perfumery groups online will be helpful. Natural Perfumery, Botanical Perfumery, Making_Fragrances, Perfumemaking are a few of them to consider.
The PerfumersWorld free introductory online course will help.
There are a number of books on the subject, but no single book will tell you everything you need to know; there's no quick-and-dirty in perfumery. You have years of study ahead of you and I hope you'll relish every minute of it :-)
I know at least one Poucher book is available for free download; if I find a link I'll post it but you can likely find it with a Google search. His books are enjoyable as history, and helpful if you're interested in 19th century-style traditional (natural) perfumery.
For another look at how a perfumer works, I would recommend Chandler Burr's "The Perfect Scent," particularly for the half of the book dealing with JC Ellena's methods and creative process.
I've heard these are quite worthwhile:
Heather has a good list of perfumery books on Amazon: