Honestly you have to make sure over and over again that you have: 1st removed all that is in the way, old adhesive and broken glass 2nd... Fit and fit again... It usually takes me 10-20 times to get that perfect fit. 3rd The Metal Bracket... You might have placed this bracket too much to the right or the left. I usually lift the lcd up to the light and put the metal bracket perfectly in the middle so that you can see the camera hole. 4th. If possible try to keep as much of the original adhesive as possible especially in the top area. Use a heat gun to take it off 5th. Always start by fitting the top portion of the lcd into the frame( that is where the metal bracket fits into frame) The metal bracket has two or three prongs that fit and hold down the glass. So adhesive plus the bracket makes the glass stay on. 6th It would be better explained with reassembly guides.
Not sure how the lcd will hold on to the thin frame., since there is not too much room in the upper left and upper right area to affix to. The other problem in leaving the frame off is that if you have broken glass near the side plastic frame there are shards of glass that have to be taken off and in taking these pieces of glass off you end up taking off the adhesive that apple originally put on the ipod If you have to put new adhesive on the 3m adhesive is not nearly as sticky and your whole screen will come off in time. The design with the metal bracket is annoying but it usually stays put. It is hard to know if this bracket is essential in the reconstruction of the device. Only time will tell if our repairs seem to come apart by themselves do to improper or lazy repair. Heat will tell in the summer and time will be the answer