Hi! You can see all the Summoning Chances in the "Info" tab in Summoning Portal. The chance of sumoning a Mythical Champion from the Primal Shard is 0.5%, while the chance of summoning a Rare Champion is 82.5%. The process of summoning Champions is RNG-dependent, which sometimes can be pretty disappointing :( I hope that next time you'll be more lucky with your pulls and will be able to get the Champion you want!

@OP    yeah man sorry to hear that :/

As you said being new to the game, I reccomend  not  buying Primal shards at early game.  If you fixed on opening shards then  maybe a good acient shard package will do the trick for your hunger ;)

aside from that well the single best deal in the game  is the monthly gem offer pack at a price that is not matched anywhere else in the game

The thing you did wrong was spend money on Primals.  They are a terrible value and you should pretend they don't exist until you are actually earning them from content.  

To be honest there are a lot of things that you can do in this game that you really shouldn't, and I'm afraid you learnt the hard way that unless you have a bulging bank account buying shards is a big no no.