Oil level

Just to be sure that you are checking it properly, was the engine running while you checked it, or had it just been turned off? Because either way can effect the reading on the dipstick. Generally, the engine should be off for at least five minutes if you want a decently accurate reading, as that gives some time for oil to drip down from the top of the engine and back into the oil pan.

It is possible that the mechanic simply made a mistake. It does happen occasionally that they simply do not put enough in. On the rare occasion that I have someone else do my oil change, the first thing I do is check behind them.

So, you should go ahead and top it off. Check it again in a few days and go from there.

Keep us posted.