They mean two different things:

Te veel -> Too much (as in, an excessive amount)

Zoveel -> So much (as in, quite a lot, but not excessive)

If it means "more than necessary" you use te veel, like this sentence.

If it is a noun you use teveel, in which case the best English translation for it would be excess, e.g. het teveel aan koffie - the excess of coffee.