Well, hold that thought for a moment.
Let's take a look at why I don't think you want your ex-girlfriend back.
I don't care if it has been one day or 10 years, absence makes the heart grow fonder. As time passes we tend to forget all the negatives and only glom onto the positives about our ex loves. Our mind focuses on the golden days of new love and romance. We don't rush to remember what separated us in the first place.

When you really sit down and think about it, whatever issue came between you and caused you to break up - well that issue is still there. Again, I don't care if it's been a week or a year, it is very unlikely that both of you have changed as people so dramatically that you will surmount whatever split you up in the first place.
Did you cheat? Did she? Something wasn't going right for that to happen and unless you do some heavy duty analysis to figure out what was wrong, you aren't going to be able to fix it.
Did you fight too much? Get bored with one another? Or did she just not love you and you loved her? Guess what? The odds of changing any of these scenarios are slim to none.
So here's what I suggest you do instead. If your heart is setting on getting your girl back, I'm not going to tell you to give up. What I suggest is that you put that plan on hold for a bit. Instead of focusing your energy and thoughts so much on your ex girlfriend, designate a time during the day when you give yourself permission to reminisce or grief or whatever. But for the rest of your day I want you to expend your excess time and money and energy on yourself. That's right. On you.

On doing something you've always wanted to do. On getting in the best physically, mental and emotional shape of your life. Do you want to spend your Saturday nights hanging with the guys watching the game? Do it. How about joining that volleyball team you always admired or taking that solo trip to Paris to drink wine and sample cheese. Whatever it is, just do it.
This is the time for you to focus on you and enjoying your life to the fullest, each and every minute of the day. I want you to sit down with a pen and paper and figure out just what makes you happy. Then do it!
Then when this process is done - in your estimation - take another look at your ex-girlfriend. If you do want to get back in touch with her - you are offering the best man you can be. But there is a really good chance that after you do this self analysis and focus, you will not want your ex back.