No, don't dump it! Wait. Patience.
Now, not knowing your OG it is hard to determine where your FG will approx. be. However, when it is done, it is done. 3 days it is not done so again, relax.
In two to three weeks you can take a gravity reading. It will likely be lower. When the gravity remains stable for a few successive days it is ready to package.
As to your concerns of contamination, did it taste "off" when you took the gravity sample? I highly doubt that it is.
It is possible for a fermentation to not produce much kraeusen and be over very fast.
Now, some advice for the future. Smacking the yeast pack really only lets you know that the yeast is still viable. Even if it does inflate and is viable, you really, really should make a starter to have sufficient healthy yeast to ferment. Especially if your gravity is up near (and especially over) 1.070.
As to re-hydrating being debatable here are the facts. The manufacturers of dry yeast may state pitch it directly on their sachets for the homebrew market, however they advise pro brewers to rehydrate.I believe they tell home brewers not to bother because a)they want their product to seem easy to use and b) it is possible to have a successful ferment pitching directly, it just is not best practice. Check their websites. While their is a large amount of yeast in those packets not all of it will successfully be revived. If you rehydrate it the viability will be vastly improved. Here is why. When the yeast is rehydrating it's cell walls are vulnerable and it cannot control what passes through them. Drop them into a batch of sugary and nutrient rich wort and many will not survive as these passing through the cell wall can increase the osmotic pressure damaging, possibly rupturing the cell.
That said, by pitching a pack of dry yeast in addition, you probably had a good amount.