I used your spreadsheet data to draw a couple of graphs as I find this makes it easier to visualise what is going on. I noticed two things.

First there is an offset at low current values - that is as the phase angle varies the current does not at first increase. If you offset your table data by a suitable amount this should disappear.

Secondly, the shape of the two graphs are very similar but the gradients differ. If you remove the offset noted above you find the measured current is about 1.4 times the expected current - looks like a root 2 factor possibly. So if you scale your table values by 1/1.4 it should be much more accurate.

Hope this helps.

Ian