Dear Iona,
you're right!
"A lot" = molto or tanto
Iona studia molto/tanto (well done ;-) )
"Too much" = troppo
Iona studia troppo.
Generally, when we use "troppo", we mean something negative.
Iona studia troppo. Lei dovrebbe divertirsi invece! (Iona studies too much. She should have fun instead!)
ps: study can be fun too ;-)
Ciao Iona