most likely you've a mistake in your phrase, it should be:
я-то представлял себе.. (note the dash between я and то). in this case то is used to specify that it's precisely you who you do speak about. that it is you and specifically you were the one who (представлял) believed/imagined/etc
я то представлял себе (with no dash) on other hand means that you did imagine THAT in some way... here то refers to something that is not yet mentioned in your sentence.
for example:
я-то представлял тебя иначе = me, my image of you was different
я то представлял себе иначе = in my mind i imagined that thing not like that
я-то думал, а он нет =me, i was thinking and he did not.
я то думал, а он не то = i was thinking the right thing (that one) and he was thinking the wrong thing (not that one).