So you are saying that you are casting a spell and would like somebody to cast the same spell on your behalf? You are also saying that you are fixing your spell to make it work better, yes?
Well there is always a chance for things to go wrong (meaning not the way you intended as an end result), no matter how experienced you may be. When two people put their energies into the same goal, it only empowers the probability of intended success! So having more than one person will always increase your chances of having the intended outcome.
The more energy you put into things, the more you will get out of it.