phoebeisis

Try this.
Put as long a wrench as you can fit on it. Position the wrench so it is parallel with the ground-more or less-and the crankarm is pointing about 2 oclock.
It helps if you have a second set of hands.
Get a hammer ,and hit the wrench as far out on the handle as possible. Strike it a sharp blow-use a heavy hammer.You don't really have to wind up to hit it-especially if you use a heavy hammer.You have to pretension the wrench before hitting it-by pretensioning it,I mean be pressing on it, so it isn't going to move relative to the pedal once you hit it.You can also use a 2x4 as your hammer. Be careful not to hit the frame.
I would spray the offending pedal spindle with penetrating oil first, and I would tap it with something metal several times in the 30 minutes before doing the above.The idea is to break up and corrosion that is binding the threads,so you have to tap,tap,tap metal to metal to transmit the vibrations to the threads.
An extra set of hands is very important while doing this.Someone has to hold the hammer,wrench, and crankarms in place while someone hits it.
Some pretty smart mechanics suggest actually giving it a tiny-tiny-hit in the wrong direction before going in the correct direction.
In any case,do the penetrating oil(anything that clains to be penetrating oil is fine-WD 40 is much better than nothing,and any oil is better than nothing-just give it time to work its way into the threads-at least 30 minutes-more is better)) and tap,tap tap for at least 30 minutes before the big,sharp rap.
Luck,
Charlie
PS-I have mis turned pedals and BB many times-most folks who aren't bike mechanics have. You might have tightened it a bit by going the wrong way initially.A sharp rap-or several-will work-100%.Careful of the frame!! Wear leather gloves if you are holding the wrench(takes the sting out if the hammer holder misses)!!