Don't be too discouraged! I had the same type result when I built my first off-center fed mullti-band wire antenna. I modelled my first attempt after the old design in the ARRL hand books for a "windom" using open ladder line (I used outdoor TV twinlead). Even with a tuner at the transciever, it was problematic... Tuning was too sensitive and loads of RF in the shack.
I re-grouped to try again... This time I tried using the dimensions and materials described for a "Carolina Windom" marketted by Radio Works. I even used one of their line chokes at the end of the twin lead. I tried several winding ratios on the balun coil I made to connect to the coax. This design was more succesful, but the performance was not as good as a dipole I used for refernce and there was still some RF in the shack. (I assume the commercial antenna would have worked better than the one I built.)
The concept of this type antenna really appealled to me because it would "fit" my QTH sitiuation so well. So on my third attempt I went back to the basics; and came up with a center fed design this time. A 20 meter Extended Double Zepp (EDZ) would fit (80 feet) and could be tuned for the other bands with a tuner. (The basic EDZ antenna is described in the ARRL handbooks.) Since it was center fed, there was no more RFI issue and I could count on all the radiation to come from the horizontal wire. This antenna worked great with a simple MFJ tuner (balanced output) for several years until a storm brought down one of the trees holding the wire up.
On my fourth attempt I got real serious! I bought an antenna modelling program and went to work on designing the ultimate wire antenna for my situation. Some of the results I came up with may be of interrest to you since they use the same materials that you already have on hand. I have documented the construction and performance of the NB6Zep antenna on my website at: http://www.teleport.com/~nb6z/nb6zep.htm
I also have several other wire designs you might like to look at before you start your next construction.
Keep trying; the answer is out there...