Psi balls and other things of such are generally energy manipulation and that in particular is indeed how spells work.
Regardless, spells are when using energy through set, strict technique that usually allow little room for errors in that they commonly are cast with energy beyond that of your own - while as energy manipulation is much more broad in it's countless techniques (besides those included in spell themselves) and are also entirely resting on your own energy or rather the energy residing in your body at the moment.
Just because psi techniques are difficult for you, does not mean that your spell-casting ability will be faltered.
Also, many times at first, psi balls can not be seen because your energy is so (forgive me for the term) weak; beginners have not yet worked much with their own energy much less casting it outwards from the body therefore not dense nor strong enough to be seen.
In that, you probably were successful you just haven't worked enough with it to really see anything.
As said above, practice is the answer here.