As said by the others, it is a hard thing to get right in the beginning. I still mess one up every now and then.
Photos would be a big help.
I suspect your issue is getting too much ground away while ding the plunge. This is often called the "2" line". Getting or making a shoulder jig ( a small stop-clamp for the blade) will greatly help.
Suggestions:
Slow down. If it takes a week to grind a blade, so be it. If it take a month to hand sand a blade, so be it. Rushing to do a blade quickly is the cause of most failures.
Get your stance right. Feet apart at shoulder width. Elbows tucked in at your sides. Grip the blade firmly and move the blade slowly as you grind. Don't sweep the blade backl and forth from side to side, but move it in a straight line until you either have the tip off the belt or reach the ricasso ( depending on which way you are going) … them lift the blade and return it for the next pass.
Slow your grinder down. If it isn't VS, then change the pulley to reduce the speed by half. A pair of 2-3-4 pulleys are a good way to change belt speed as needed.
Use the right belt. Start on a coarse belt for material removal. 80 to 100 grit is a good one for new makers. Stop when the bevel is about about 75% shaped. Move to a 120 grit belt to clean it up after you get the basic shape. Most of us quit there before HT, but you can go to 220 if you wish. Once the blade is HTed, go back to the 120 belt and get it flat and perfect before moving up to 220 and 400 grit. Most makers quit there or move to hand sanding. For a new maker, I suggest stopping at 400 grit.
Do a couple blades with a file and sandpaper only. This will help you learn how the bevel forms and where to take away metal.
Start simple. Many new makers want to start with a Bowie knife or other more complex shape/size knife. Start with a drop point hunter with a 3" blade and a 4.5" handle. Keep it simple with no embellishments and basic full tang handle scales
Use drawings and photos as a reference as you work. Have the sketch or photo out by the grinder to compare to as the blade takes shape.
As aid before by the others - Visit a maker who can show you how it is done. Watch him and then try to do some grinding with his guidance. It is worth a 2 hour trip and a six pack of beer to get that type help.
There are hundreds of You-Tube videos and DVD's for sale on grinding. They can be a valuable resource.
Use the Custom Search Engine ( in the stickys) to read older threads on grinding bevels and other grinding issues.