I don't want to go into too much detail or make this a sob story or anything because I don't expect positive responses here anymore. But basically, I was raped in 2016, and ever since then saying no has been a serious internal conflict. There are times where I feel physically incapable of saying the word, and I feel like it's my fault for even wanting to say it at all.

The biggest moment where I feel like I can't or shouldn't be able to say no anymore is when a guy is already turned on and hard. There have been times where I've been on first dates and strictly told myself before the date that I wouldn't do anything sexual (after being raped that was a problem for me, so my counselor told me to practice establishing boundaries with myself before a date). But then, as the date progressed, the guy would want to kiss, which I'd be hesitant to do but eventually give in, thinking it's only a kiss. That would then lead to making out, which I justified as being fine as long as it didn't go any further. But then lo and behold, before I knew it, he would be trying to guide my hand to places I didn't want to go and would be confused about why I was resisting.
This makes me feel like it's completely my fault, because if I didn't want to touch his dick, why would I have kissed him in the first place, right? I feel like, once the guy is hard and horny, it's on me because it's my fault he got to that point in the first place. If I would've just said no to the kiss, it wouldn't ever progress to this point, so now this is my problem, not his.

I don't know. Now, I do have a problem with saying no even for little things, like kissing. But it just seems like after a guy is obviously turned on, it amplifies my concerns about saying no. I think it's because I feel like when it's just kissing or something small like that, he will be more receptive and use more common sense if I don't want to do that and say no. But after he's turned on, I feel like all common sense goes out the window and all he can focus on is that he wants to move to the next step. I know it sounds like a gross generalization and I am hoping that it's not true for most guys.
(And just to show how this isn't just some little worry in the back of my mind, and that it's actually a pretty severe, obsessive thought process that takes over whenever I'm in this sort of situation, the simple act of even writing about this caused me a great deal of anxiety throughout this post. Over the course of writing those past two paragraphs, my whole body was shaking and I could feel my heart rate speeding up and there was a horrible tightness in my chest. I actually needed to take a break to calm down and I needed to let the anxiety stop on its own time, it wasn't something I could control. So no, I'm not overreacting. Anyone who has experienced those things knows that they are extremely uncomfortable and scary to endure and that they take over.)

I already feel really stupid about writing this, and I know my concerns are probably childish and immature and all I need to do is grow a pair. Growing a pair isn't exactly an option until I can understand how to deal with this and reason with myself first.
So what I'm really wondering is how can I practice saying no and even force myself to say no in situations like that, without the fear of being forced to do something? Being raped is always the number one concern in the back of my mind during these encounters. If my only concern was that I would be disappointing the guy or that he would never want to see me again, I could deal with it better. But my biggest fear from saying no is that he'll either get angry and hurt me or get pushy and force me. 
And before I get called out for throwing a pity party or wanting to be a perpetual victim, I'm writing this in search of help because I'm actually really fucking tired of feeling like a victim.