Hola Marc

To say "everything" we always use "todo" (masculine singular form) if we are just referring to a group of things but think of it as a neutral unity (everything). There is a note at the end of the lesson explaining this. 

We would is toda (feminine singular form) if the referent we have is clearly a feminine noun, for example:

"-¿Has comido tu pasta? - Sí, la he comido toda."

(-Did you eat your pasta? -Yes, I ate it all/ I ate all of it)

or

"He visto muchos monumentos en Roma, y me ha encantado todo."

(I saw lots of monuments in Rome and l loved everything/all of it.)

You could also say "me han encantado todos" if you want to refer to all the monuments, using the plural. But you could equally refer to the unity of all the monuments as in "everything" and then use "todo", which is what I did in the sentence.

I hope this clarifies it.

Inma