Parallel transformer output not expected RMS value
Looks like your oscilloscope input is saturating. The input will have a certain range and beyond that you need to add attenuation (as in a x10, x100 etc. probe) or you will get that effect (and can possibly damage the oscilloscope at some point, though most should be protected to a couple hundred volts peak or so). 

Try a x10 probe (and change the software setting to get it to read right, but that's not as critical).