Well stability is often an individual issue. Lots of play boaters and racers think stability is last on the list of boat traits when compared to turning ability or speed, because these paddlers rely on bracing skills to keep their boats upright. For them, the boat stability doesn't matter; it is all about the stability of the paddler. However, these paddlers cannot let go of their paddle and take a picture or their boats will often go right over. When I see the fastest paddler I know, he is working very hard to brace his boat and keep it upright in the calm water of the launch area. He claims that speed really helps stabilize his boat. I wouldn't have a clue, because after he takes a few strokes he is out of sight. At a distance he looks like he is eating up the lake at about 10 MPH!
For me, having stability is a good thing. It lets me rest and get a drink or a snack. It lets me put down the paddle and take a picture. And it is faster in the long haul because I can concentrate on my forward stroke. So if I'm paddling a little sprint of a few miles then a tippier boat is fine, but for all day paddles I want a stable boat. The funny thing is I think almost every boat is very stable. Only the skinniest kayaks are not stable for me, but you will feel differently. So try the stability test when you are trying a new boat.
In calm water sit on the back deck and put down the paddle. Now cross your arms. How do you feel?
If the boat is too tippy you can make up for it by lowering the seat, improving your balance or adding ballast. Lowering your seat may change the fit of your boat in ways you do not like, improving your balance is the best way but it takes a long time and lots of training. Adding ballast is quick and easy if you do not mind the extra weight. Usually just 8 - 12 pounds of ballast will make a big different in how stable a boat feels. The best material to use for ballast is water because it has neutral buoyancy so it is heavy but will not cause a flooded boat to sink. Optimally you want the weight very near your seat. In a canoe right under the seat might be good but in a kayak you'll want it right behind your seat or right in front of it. Sometimes paddlers put it just in front of their foot pegs.
Securing the ballast is very important. If the ballast can move around then it can make the boat less stable instead of more stable. You can tie the ballast in place or wedge it in place. I have had the best luck with wedging the ballast in place with inflatable flotation. Kayak float bags or even snorkeling float vests work well.
To contain the water I've used hydration bags and 2 liter bottles with equally good results. In a Sit on top or other kayak with a higher seat you can often fix a water bag under the seat inside the hull. This lets you carry your water in a place where other things will not fit.
SO if your new boat still feels a little tippy after the first 10 hours or so, try some ballast when you are planning long paddling days. As you get better balance you may decide you need less ballast.
If water will not give you enough weight for ballast you may like to try something heavier. Check out the link below for another ballast option: