I wouldn't risk the bettas health by getting a new frog
.
It is extremely difficult to keep the water conditions optimal for even for the betta. Just thinking about what is best for the fish (and the frog).
If the wormcube is too big, just get a small chunk out of it, never unfreeze it and the freeze it again, you might end up poisoning the betta .
It is always best to get all the testkits.
good luck with the betta!