Is there a way to fix a polyurethane mistake?
There are almost no finishes that are totally colorless (although poly does have a slight yellow tinge, more than some other finishes). Also, most wood changes color over time with exposure to light and oxygen (typically getting darker).

Frankly 2 coats of polyurethane is only the bare minimum. Particularly if this is a kitchen or dining room table that will get a lot of wear, you will want it to be durable. (Maybe for a side table 2 coats would be OK). If this were my table I would say put a 3rd coat on it and leave it for a few months to see how you feel about it. It's not going to be any easier to strip &amp; sand it now, so you might as well see how it ages.

If you do refinish, maybe try a water-based acrylic, that will be almost colorless. There are many sites online that compare the various types of wood finishes, e.g.: http://www.diynetwork.com/home-improvement/whats-the-difference-between-polyurethane-varnish-shellac-and-lacquer/index.html