Well, there's two parts to my opinion on this one. The first is, understand that there is no 'magic pill' to make this part easier, really. There's certain things you can do which help the transition/state but ultimately it's up to you to grab your nutsack and step outside your comfort zone. I say this because I am very familiar with the problem you are describing, having both conquered and fallen victim to this scenario in the past. And I know that what's really holding you back is a lack of confidence/desire to protect your ego from feeling damaged or rejected.
You have to make a conscious decision to try something new, and roll the dice a little bit. Understand that if you fail to pull the trigger when you have a girl sitting on your bed in your room with you, you will be branded in her mind as the worst kind of sludge there is... a coward. I'm telling you man, I've been in that situation before, and they can almost get insulted by it. Freezing up like that when the green light is obvious shows a glaring lack of either social intuition or bravery, neither of which is going to score you any points with the opposite sex. So keep all that in mind, and figure out for yourself which is ultimately worse -- being blown out while you try to take what you want like a man, or protecting your precious ego and losing out on potential life experiences in the process.
All that being said, there are some small things that you can do to make the final physical escalation a little more smooth. Primarily, you want to be having lots of kino happening freely between both parties obviously. A thing I like to do during escalation is the "high-five" where you let your fingers intertwine afterwards. I'll do this usually to reward something good, like her demonstrating interest or being flirty/using good kino, etc. Just be really in tune with her reaction to your touch. If you sense that she's really comfortable with it, you'll usually know. One the vibe is on, it's ON, and then you'll realize "ooooh yea" :-D It's one of the greatest feelings when you're communicating clearly non-verbally and you know you're "in". If you've both been touching each other a lot, it shouldn't be too awkward at all to try a playful kiss close on her. Then once you're making out, I don't think I need to tell you where to go from there.
Hope that helped. Good luck.