I set up an amplifier (LF351) for a gain of 5.7, but it is saturating. Do I have to utilize the offset null pins?
LF351 doesn't have rail-to-rail input capability, not even close.

With +/- 15 V supplies, the minimum common mode input voltage is specified as -11 V, with typical operation to -12 V. Translated to your +10.5/-0V supplies, this means you need to keep the input common mode voltage above 3 V (if you want to fuss around and take a risk) or 4 V (to be sure it will work). 

You should either use a wider supply range (+/- 12 or +/- 15 V) or choose an op-amp better suited to the supplies you have.