Too early to resign?

Did my opponent resigned too early in this game? I knew I was atleast 10 points ahead, but was not very confident about the outcome.

And also, how could I have improved my opening play in this game?

As you say, Black is ahead, and I don’t think White could have made up the difference up top, where most of the remaining undecided points lie. So the resignation was justified and highly honorable since White did not play on in the hope that Black would make a ridiculous blunder.

You could improve your opening by taking another open corner and extensions before starting a running fight.

On 19x19 boards I find it more easy to move to another corner before starting a fight, but on smaller boards if couple of stones are already there it is very difficult to win fights later during the game.