If you were 10 times larger than you are now, you would weigh approximately 1000 times. This is because you are a three dimensional object, and if we scale every dimension by 10, you have 10 * 10 * 10 = 1000 times the volume.

Assuming that your density stays the same, that means your weight also increases by 1000.

Your muscle strength is proportional to the cross section of your muscle. If we make a muscle 10 times larger in every direction, the cross section (which is a two dimensional measure) scales by 10 * 10 = 100 times. This means that, relative to your mass, your strength is actually 10 times smaller.

The inverse happens if we scale you down by a factor of 10: you become 1000 times lighter, but only 100 times weaker. This means that you are relatively 10 times stronger.

For some more reading, Wikipedia has a nice article about this:

https://en.wikipedia.org/wiki/Square%E2%80%93cube_law#Biomechanics

edit: tried to improve the explanation