Fronush- welcome to the forum.
I have a DBRC (sorry, the abbreviation is easier to type) and I use it whenever I feel the need for an enema because I have retention issues. You didn't say what size balloon you bought. They come in 3 sizes; 250cc, 500cc, and 750cc. For most average adults, the 500cc should do the trick.
The material your DBRC is made from will determine which kind of lubricant to use. If it's latex, use a water-soluble lube, and not a petrolatum based one. My trick is to insert the first balloon completely, right up to the hilt of the second balloon and then inflate the first one. It should be snug, but not uncomfortable for you. It it's not fully inflated, it will leak. If it's overinflated it won't be comfortable when you use it.
Once the first balloon is inflated, begin to inflate the second one. As it inflates, you will feel the first balloon begin to move towards your anal sphincter. That's okay, you want that first balloon to "seat" snugly against the sphincter. Once you think that first balloon is where it needs to be, stop inflating the second. You might add one more puff of air to the first balloon, just to be sure, but you shouldn't need much more than that.
Now, relax and enjoy your leak free enema. I would recommend taking a small volume enema with nothing more than salt or baking soda in it the first few times, just to get used to it. And don't try to set a new retention record just yet. Give your body a chance to adjust.
Play On!
LadyDoc