Is my wood stain going to match?
Matching stain is very difficult. Seriously, I heard of one guy who markets himself as the "Wood Whisperer". When guys start calling themselves a wood whisperer, you know you are getting into the black arts.

Typically the average floor installer will use a wood wheel from his manufacturer and pray.

That said, you will not know how good the match is until it ages a little bit and fades, so you have to give it some time. Basically, what this means is that in 3 months if it still doesn't match you can call the guy up and yell insults at him.

You cannot "fix" a stain. You can try re-finishing, but you are rolling the dice even more on that one, because then the wood wheel will not work anymore. The wood wheel is only for fresh installs. Refinishing requires a "wood whisperer". Also, refinishing is expensive because it involves sanding.

Note that finishes can vary under different lighting conditions, so that a finish that matches in daylight, could look totally different at night under incandescent or fluorescent light.