Interview and background check?

[Illini1]

Long story short.  I applied for a position at a company that I really wanted last summer but did not get it because from what I'm told they promoted from within.  So I continued the job search and accepted a new position at a different company at the end of January of this year.  Last week out of the blue a recruiter called me from the company that I interviewed with last summer and asked if I was interested in a different position within the company.  I of course said yes as it would be about a 30% increase in pay with much better benefits.  After a few questions by her she asked if I was I was still employed with the same company as I was last summer during my initial interview (she still had my old resume on file).  I sort of panicked not knowing what to say and I said yes I was.  Anyways, everything went well with her and now I have a face to face interview with my potential managers (she won't be there). 

Do I update my resume and include my new position which I have only been at for around 2.5 months?  How would the future employer feel about such a short stay at my current position? Or do I just go with my old resume and hope that my new job doesn't appear on any potential background check?

If I do include my new employment how do I explain me wanting to leave after only 2.5 months?  Also, if it came up how do I explain my saying yes to the recruiter as to being still employed at my old employer?

I know I might be putting the cart before the horse here as I still need to do well at the interview and get an offer.  I would just hate to get the job offer and then only have it taken away because of  a red flag on my employment history.

Any and all advice would be appreciated.

[pbkmaine]

1) You very much wanted to work at potential company, but were turned down, so you are excited to get this offer.
2) In your excitement, you may have misheard the question the recruiter asked. When you were turned down at potential company, you took another job. But potential company has always been your first choice.

[mozar]

Or do I just go with my old resume and hope that my new job doesn't appear on any potential background check?

No, don't do this. It's fine that you took a new job, and it's fine if you leave only after 2.5 months. It sounds like you're young, and moving around is expected. Now if you change jobs every 3 months for the next 3 years, that would be a red flag.

Just say the new job would be a better fit, or better future potential, whatever you want to say. It's not a big deal.
You can update your resume with your new job, but I wouldn't give it to them unless they ask for it. The experience of your current job might even help you at the interview.