Well, you can't be thinking that you'll land all three and he'll stand there and take it Just for fun let's run through a couple of scenarios you might work through.

You jab, jab again. At some point he'll try a right over your left- pretty likely, yes? When he does you stiffen your left arm to "leverage" his right up and away from your head while you drop your weight to your right leg- tucking your head behind your left shoulder- then throw a right upper cut to his solar plexus and a left hook to his liver. To get out, get your right glove behind his left elbow and turn him to your left while you step out to your right.

Or, you jab then feint the jab to draw his jab. When he jabs you slip inside it with a short straight right to the heart, then weave to the outside while hooking his body with your left. From the outside you straighten and cross your right to his head and follow with a left hook.

See the idea? You always work your way in and out, always imagining a response from a guy trying to win. Don't just stand there and punch.