If, after loading your jars into your canner and bringing it up to a boil, it maintained a boil for the entire required processing time - the canner is not the reason your jars did not seal.
Boiling water canners do not have a flat bottom for a couple of reasons - the bends in the bottom add strength without having to use a thicker metal (which would make the pot heavier and more expensive), and it prevents the bottom from warping.
There are two reasons for not using a boiling-water canner on a flat-top glass/ceramic cooktop. One is how heat is transferred from the heating element to the pot. Without a flat bottom in contact with the surface of the cooktop there can be problems with the heating element ... uneven heating which can lead to heating element failure or developing hot-spots.
The other reason (which in some cases is the main reason) is weight - a 21-qt boiling-water canner weighs about 7-lbs empty, water weighs 8-lbs per gallon, then you add the weight of the canning jars, the food in the jars ... a fully loaded water canner can easily weigh 45-lbs. An empty pressure canner weighs about twice as much as an empty water canner.
Yes, you can use a pressure canner for boiling-water canning - you just leave the lid off.
IMHO: I would start by reading the information that came with your stovetop and see if it mentions anything about canning, or call the customer service line for the manufacturer of your stovetop and see what they have to say. They are constantly being improved - the old ones all said not to try canning on them ... the new ones might be different.
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain