the dream i don't think you have to worry. it could be showing you a desire, or rage towards the person. i don't think you cast anything over them. an option could be [slim] you unknowingly projected into their dream and attacked them. this is a slim chance, but some people have been known to astral project without realizing. i have on occasion.
the cursing people to die, be careful what you wish for. if your hatred is strong enough, you can cast a spell that can kill another. this is rather dangerous for obvious reasons, if it's successful they die, if it backfires you will get sick and possibly die. now that this has happened though, you're probably going to receive a lot of negative effects if you cursed them and they died as a result. not little effects either, your punishment won't be a broken pencil or a lost remote control, i know people who have cursed for fun, as well as cast a death curse for revenge, the results are severe. injuries, divorce, loss of friends, loss of job, miscarriage, sickness, these are just a few things they had to deal with.
if i were you, while you cannot change what you've done, i'd try to do some good. this won't erase what you did, nor will it stop karma, but volunteering, cleaning a park, donating to a charity, and so on might help even things out a bit. you should also meditate long and hard not only why you cast these spells, but the next time you're going to cast any type of spell, stop and ask yourself if it's necessary. sit and meditate on the issue. i don't know how old you are, but i'll assume you're a teen, your emotions are all over the place right now. when i was in high school there were times when i wanted to curse people [and my one friend gladly provided me with curses] the thing is, i would wait a week, meditate every day on if the curse what necessary. each time, when the day i was going to cast rolled around, i found myself unwilling to do it because it was not needed. point is, think before you do because you reap what you sow. [idiom, basically do good get good, do bad get bad]