Relax! Relax! You're not any fatter because you weighed yourself on your bf's scale rather than your own scale. It doesn't really matter whether you are 126 or 132 because these are just numbers and the important thing is how you look and feel. *Your actual body is the same regardless of what the scale says!*
I had the same dodgy scale for about 12 years. I knew it was off but I figured that it doesn't really matter because all of my weight gains and weight losses have been measured on that same scale. I recently bought a new, digital scale that is pretty accurate and I've been weighing myself on both each time so that I don't accidentally mistake the new scale's numbers for a gain
Just pick a scale and stick to it, and don't fuss about a little inaccuracy.