Big A is correct that you need to get with someone experienced to help you learn the mandatory poses -- no matter how good your physique really is, the judges will not have time to look past this level of presentation to see what you actually have.
Second...find a different show. If you are 12 weeks out, then getting from where you are to contest condition in that time period will involve far too much loss of lean body mass while losing the fat/water you are presently carrying. You would wind up scrawny and probably very flat from the loss of muscle, and also probably the skin would not have time to tighten up properly and give you the look of good conditioning that you need to do well. You should be on a 16 - 18 week diet plan so as to hold as much lean mass as possible while losing the fat/water.
Third...find someplace near you where you can get your body fat tested (calipers method is okay) and then have the SAME PERSON do it about every 2 or 3 weeks as you diet so you have an idea whether you're losing LBM or fat/water. The absolute numbers don't matter a lot as every person doing the procedure will probably get a different reading -- what matters is the trend and what it tells you about composition.
Ken