Taking it 4 is not really that bad. I am never a fan of the idea of canceling a score. A lot of folks thing they were doing terrible and ended up scoring very well. Thinking you are doing bad probably means you are getting harder questions.
There are people who take it a lot of times and get into top schools. If a school wants you they generally wont care. You can always self report your score since they only want the high and if admitted send them your official score...if the schools allow that.
I hate to say it but chances when you are at the bottom of the 80% range are nearly impossible at top schools. The people that get in with those scores have something far more impressive that the adcoms want than a score. If you happen to fall into a fairly common and competitve demographic a low GMAT can definitely ruin any chance. Now if you are a minority female with a very interesting story it might be a lot easier no matter the score.
Retaking with a 700+ is a double edge sword. If you are 100% sure you can improve 30+ points go for it unless you are at the 740+ range then its probably a waste of time unless you have nothing better to do. I know several members on here retoook with 720+ scores and jumped up 30+ points and managed to get into top schools. Not saying that they wouldnt have gotten in with a 720 or 730 but it obviously didnt hurt them. If you arent applying until next year and know you can bring it up into the 740+ range, I dont see the harm in it. If you are trying to apply this year then dont waste the effort...