Q:

I lied about my job title.  Will that affect my background check or employment verification? 

Let me be candid.  I have worked as a software Engineer all my career with 2 years of product management experience (did a startup 4 years ago).  I wanted to switched to PM full time but was not getting calls due to lack of experience.  
Since I am very confident in my PM abilities, I decided that I pose as a PM in my current company, upped my experience to 4 years on my resume and started interviewing and I got job offers almost immediately. 
I know I lied since I did not get any interview calls for many months and did not see a way out.  But I am now afraid of the background check.  All other details like dates, salary, other employment history is correct.  

A:

How likely that I will get caught?  

If the background checking agency does their job well, you are almost certain to get caught.  You probably already knew this before you padded your resume. 
Your best bet is to own up before the company finds out from the background checker.  They will likely rescind the offer, but there's also a small chance they might let it slide if you impressed them in the interview.  
If they find out from elsewhere, however, you will almost certainly lose the offer.  Even if they find out later after you have started working there, you are likely to get fired or at least disciplined for lying on the resume.  
Also, stop lying on your resume immediately.  As you might have realised, it will likely get you only as far as an offer.