Come on, take the flying lesson! You will regret it later if you don't. In about 2 years you will be at a party, some guy will say "Hey, I flew a plane once" and all the women will flock to the fly-boy. If you say "I got a flying lesson, but didn't go cos I'm a big girls' blouse", they'll definitely not flock.
When you were at the gate getting on an airliner that was going to be 7 miles up. At least in a light aircraft you're only a few thousand feet: less far to fall
But honestly, there really is little to be afraid of. You know in the movies when the engine stops on the plane and it starts screaming and plummeting towards the earth? Load of knackers. Let's say the engine dies. You are a few thousand feet up, so even if you can't get it restarted, you have a good few minutes to have a look at the countryside, find a nice big, flat, field on which to glide down to land. Of course the experienced instructor would do all this.
Summer is the best time of year to do it, no cloud. So you can go higher, the air is clearer, and you can see further.
Quite likely, you like to be in control. How uncomfortable do you feel if you are given a lift by a mate who thinks he has the skills of Schumacher, but is really as good as Maureen off driving school? Being a passenger is scary, but when you have the yoke in hand then you are the one in control. It's a lot less scary.
Come on, be a man! Do the lesson! Or we'll all have to start calling you "poofy Ian".