OG too low?

The beer will probably be OK.

You don't give the sugar/water quantities. Assuming the sugar is correct for the amount of water - the SG reading is probably the problem.

I'm assuming you are using what they call no-boil or partial boil . . .

For accuracy, the concentrated wort and water need to be mixed thoroughly. It isn't easy to get it mixed well. The wort has a much higher SG and will want to sit on the bottom of the fermenter. (like any sugar syrup that is poured into water). Stir the wort with a vertical rolling motion, or rock the carboy for 30 minutes or more.

It still won't be mixed well - but well enough for beer and to give you some idea of the starting SG. There should be a chart for your hydrometer to apply a correction factor. As the temperature of a fluid increases it expands, so the specific gravity drops as temperature increases (same weight of fluid, but volume of fluid increases - supports less weight - objects float lower, gravity drops)

For initial gravity the correction may be important because the temperature could be higher than normal. For final gravity the temperature correction becomes important to distinguish small changes.

OT ever seen those Plimsoll (Samuel Plimsoll, 1824-98) lines on the hulls of ships? vertical line around the bow with numbers and one or two horizontal scales? They tell the ship's master how buoyant the ship is with its cargo and the liquid it is in (there's a fresh and salt water scale for some vessels). As the water warms the ship rides lower - cold water, the ship rides higher. (ditto salinity - more salt, higher gravity, ship rides higher) The master cares about that because it determines the safe load limits for the vessel, but the ship and your hydrometer float behave the same way.