"When Jehovah’s love moves you to love him in return, what should you do? (1 John 4:9, 10; 5:2, 3) You should approach God in Jesus’ name and tell him in prayer that you want to be his servant, that you want to belong to him. In this way you dedicate yourself to God. This is a personal, private matter. No one else can do it for you."
(No one should force you to do this either, would it be a "Personal", "Private Matter" if they did?)
Don't do it matey, especially if your hearts not in it. Would be the biggest mistake of your life. I'm sure you really love your GF, but if she really loved you there's no way she would be forcing you to make this unbreakable commmittment. It's one thing to get married, but a whole other kettle of fish to take the plunge and get dunked. Seriously, you're a smart man for having serious doubts about this sect, if you need more affirmation on that front you only need to browse around this site and see the major holes in the JW teaching, not to mention the completely unhumanitarian nature of the GB and their programmed drones. Don't do it mate, it's not right for you. Only you can make the ultimate choice, certainly your GF has absolutely no right to pressure you into it. Besides what would she gain from it?? Sorry to be all fatalistic, but you'd be lucky to last 2 years as a JW before the wheels started to fall of your relationship/spiritual wagon with the feelings you currently have.
All the best and once again...DON'T DO IT!. Take care yourself, Frog x