Err on the side of too much

Most new guys are afraid of scaring women off, so they end up playing it too safe and fail to get sexual attraction. It's usually better to come on too strong and then calibrate downwards. In this way you quickly find out where her limit is and you demonstrate what kind of guy you are (meaning there's no confusion about what you want from her). The only exception is if the woman is on the move (eg. on the street), in which case you want to come in more relaxed until you've gotten her to stop, after which you can ramp up the interaction.

This is your mental block, right here. You are under the mistaken belief, at the moment, that women don't enjoy sex for the sake of good sex.

In fact, they LOVE sex, probably more than most men. They can have multiple orgasms, why wouldn't they?

When a woman just want some new dick, the "guy who only wants them for sex" is exactly the kind of guy she looks for. She is far more sexually predatory and calculating than men are. She knows exactly what kind of guy she wants, what kind of experience she's looking for. The more experienced she is, the better she is at getting out of her own way and just enjoying the seduction unfolding into sex.

In fact, if she just wants some new dick, showing any sign of stability, kindness, responsibility or boyfriend potential will disqualify you from fucking her quickly and easily​. She wants a guy who makes her pussy wet and literally nothing else matters.

classic mistake, which happens every now and then even to seasoned seducers

you should always escalate a bit faster than what she's comfortable with - you're setting the pace, and based on how fast she follows (or lags behind) you adjust your tempo and slow down or make takeaways

in your case the opposite happened - you were lagging behind, so her BT (buying temperature - I like your "engine" analogy) dropped and her ASD kicked in which caused all these rationalisations and talks

next time you find yourself in a similar situation start escalating super fast until you reach the level she's slightly uncomfortable with and then slow down a bit - in your case an instant make-out in the venue could have been just about that level

Find one thing outside of your comfort zone, do that one thing repeatedly until it becomes comfortable.

For example, too afraid to escalate? Escalate on the next 10 girls you meet, see what happens, then your comfort zone is expanded

2) You're afraid to sexually escalate

The rule of thumb is, a girl who likes you will NEVER write you off for escalating.

You need o find out ASAP if the girl is at least comfortable with the idea of fucking you.

If she isn't then it's goodbye.

The easiest way to reveal true sluts / girls who fancy you, is to sexually escalate early and agressively.

Genuine sluts will be comfortable with it, infact they get turned on even more by your boldness.

While frigid girls/ girls who don't fancy you will run a mile.