I had the same problem when I got in a boat that was too big for me and I was fortunate enough to get some good instruction from really good paddlers. The most Important aspects:
1. When you initiate your first stroke on your double pump, think about pulling your stern deep into the water, this will give the pop you need to get you bow under.
2. Make sure that you are leaning far enough over your rail, if you aren't leaning enough, you are trying to push too much surface area of your boat down, the more vertical your bow is to the water, the easier it will enter.
3. probably the most important step is to have both blades flat on the water when you go to throw your bow under. This will rotate your torso and your boat will have to follow directly under you. Also, if you have both blades on the water, there is a better chance that you are far enough over your rail. and your blades will be ready to steady you once you are up.
4. Lastly, think about pushing the nose of your boat down with the up-side foot. so, if you are throwing a bow stall on your right side, you will be pushing your boat through with your left foot.
good luck, bow stalls feel really good when you get them.
check out our video on how to loop.