There is absolutely no way to guess a recipe's OG without knowing the particulars of the recipe.
Likewise, suspended solids won't affect the reading by a significant margin unless they are actually bound to the hydrometer itself.
There are several things that could effect a hydro reading. Did you add top-off water before you took the reading. If so, there's a good chance the water wasn't mixed thoroughly.
In any case, 1.120 -> 1.020 is not particularly unlikely. For your OG to be fifty points above target, however, is strange. How did you measure your volumes? If you ended up with a much smaller final batch size than the recipe planned for, this could also affect your OG.