Accidentally hurt my gf. Can she have me arrested?

Only you know whether you accidentally knocked her down. If so, then accidents happen. If not, then that's another separate problem you should address with yourself. EITHER WAY you two need to communicate better about ways to discipline your child. It sounds like its disastrous right now because clearly you two aren't seeing eye-to-eye on this subject and its causing much more serious problems. Also, when parents don't agree in front of children on terms such as discipline, it causes the child to see one parent as inferior to the other. Take my advice, get a counselor, communicate.

I am not buying that this was accidental. I think you meant to block her and you were NOT doing it in a way so she wouldn't get hurt. You didn't care how you blocked her because you were angry.

no finger prints no officers

According to the "Rule of Thumb", as long as you did not strike her with a stick wider than your thumb, then you should be in the clear. 

You bumped into her and that made her fall face first onto the floor? I agree that is harsh just for spilling water but I am feeling like there’s more to the story we’re not hearing. 

Unfortunately I believe she can. My mother and my father had an argument. She instigates him a lot and he tried to get some space from her and move her. She lost her balance, and she had the tiniest scrape on her knee. She called the police and told them he hit her, I know he didn't though because I was right there and would've heard it. The cops came, took her statement and called him to turn himself in. He paid bail and they are divorced. I told her she only called the cops on him because she wanted to be petty. She confirmed it and I have been disgusted since. Idk what happened to that case in court but I'm sure it's something you can fight. It depends what state you live in too I believe. I also tried to defend him when the cops came saying he really didn't but their job is to just listen to her statement and file her charges. Really twisted if you ask me, I thought my statement would matter, but maybe the cops in my town are as sht as I know em to be.

How I have 2 thumbs down is beyond me lol. This is literally my experience, there's nothing to dislike about it. 

spanking is child abuse. You are both awful and need help 

I'm so sorry that your gf has to be violent around your son and he doesn't deserve it at all. He's learning and growing. Child abuse is never the answer. Ik how it feels because my mom got arrested for child abuse years ago. Plus two wrongs don't make a right. Just pray that you won't be arrested and if you do, I hope you get custody for your son.🥺😔😊

Unfortunately yes, she can call the cops and it will be her word against yours.  Your only hope will be to tell the truth - which if believed - will more than likely put your family under the State microscope.  CPS may get involved and who knows where that goes.

That said - as hard and painful as that might be - and regardless of whether or not CPS or the cops end up involved - you are LONG over due for a conversation with your gf about her anger issues.   Personally, there is nothing 'wrong' with the occasional spanking for disciplinary reasons - but NEVER EVER in anger and certainly not over the trivial.   Your gf needs help in getting her emotions under control and to establish a system where she "buffers" the child's transgression(s) with time to react calmly and unemotionally.   She will find she needs to spank your son less if she does not give into her emotions.

IF she cannot get control of herself - she WILL lose her son - if not to CPS, then to the boy writing her off and ignoring her as he gets older.  

Hope this helps.  Good luck.

Mama bear be mad.