This is the best site for learning how to build your own kites. Good tutorials, decent forums (quieter since the site’s founder died) and a great encyclopedia of techniques and materials. Their best asset is the stash of plans submitted by users for almost any type of kite.
(Kite making supplies can be found from the previously reviewed Into the Wind.)
There’s no such thing as kite fabric! Just about any fabric will work… including the fabric grade Ripstop you chose. Was it difficult to sew? It is probably pretty stretchy eh?? The coated Ripstop often used by most builders on this website is coated with a finish that reduces stretch and porosity. It is also pretty light weight, probably about half the weight of the cloth you used. So… your kite will probably require a little more wind for optimum performance… but if balanced and bridled properly, it should still fly.