When you have the egg laying on it's side in the egg marker, and you have marked the middle for the cutting line, I moved the pencil up to the level where I wanted the oval and drew the oval. I tried to do a clean cut with the blade being horizontal like the egg oval.
Much like if the egg was sitting on your desk and you sliced it with a bread knife horizontally in the middle and then moved the knife up to the first third and sliced again. I do not cut with the bit straight down into the eggshell but at a right angle.
Hope you can follow this concept. Then when you lift the oval out you just turn it upside down and since the edges are flat it won't drop through the middle.
Do you sew? Well I do. Have you ever noticed the corking edges on furniture cushions? I took a piece of cord/shoelace will do it, covered it in the satin burgundy colour material and sewed it tight against the cord and left about 2" edging.
I hinged, then painted the egg. dry. Then place the cord covered material glued around the oval piece and wait till very sticky dry but moveable. Then place the whole works onto the shell and glue the sucker down!!
On the inside under the lid, snug pull the satin so the cord is in the trough/edges and let dry over night. Then inside the lid cut off the excess material. Then I put a bit of quilt batting glued to the underside of the oval to soften and then lined the inside with the burgundy crushed velvet material.
Back on the top, I glued in a cord of shinny gold beside the burgundy and on the inside of the oval glued a thin line of ribbon with the picot edge.
This will give a perfect oval relative to the egg regardless of the shape of the shell. It allows you to then cut a "slice" off the side of the shell if desired and reverse back into the recess. If you try to do this with a template you will notice that the ends "dip" - using this method avoids this. Divide you egg into 4 to find the centre top & centre bottom (you really only need one of these lines but this will ensure that your markings are even)
Using one of these lines only (ie - the halfway line) mark an equal distance towards the top of the shell. For example measure 3/4" from the line and mark a small dot. Move along the side line about 1 1/2" - 2" and measure and mark 3/4". Do this all around the shell then join up all the dots. You will notice you have a perfect oval on the top (or bottom if desired) of the shell.
To reverse the slice cut off the shell, turn the cut off piece curve side up on a piece of waxed paper. Next apply 5-min epoxy around the edge of the remaining shell and turn the larger piece over and line up over the oval pice on the waxed paper. This should fit neatly keeping in mind the varying curves for the top and bottom of the shell. Leave the shell on a flat surface and allow to dry thoroughly, then remove from the waxed paper. If necessary any small gaps can be filled with Egg Repair, That White Stuff or modelling paste for a smooth finish.
Forgot to mention this - the larger the measurement from the side line (for example using 1" instead of 3/4") the smaller the oval. The same thing also applies (and will give the same result as doing this) if you use your egg marker. I have the Natalie marker (the blue one). To mark ovals with the marker position your egg in the marker and then turn the marker onto its side. Position your pencil ABOVE the halfway position and lightly draw a line around the egg. Do not use too much pressure as this will cause the pencil to ride up on the curve of the shell.