Pamestique 

1) walking is still exercise and 2) how you improve each time you tackle those hills is a measurement for you.

I love to mountain bike. On a weekly ride there is a hill that for 6 years, I have had to walk but each time I tried it, I got alittle closer to the top. I eventually was able to ride all the way. You have no idea how great that was and how wonderful I felt. "It is better to have tried and failed then to not try at all". Keep challenging yourself.., don't stop.

Just some advice: I finally made my hill by perfecting technique, not strength. I am plenty strong, that was never my problem. What I lacked was the skill and technique to climb the hill. You need to disect why you failed... are you trying to muscle up each hill and then run out of stream and have to walk? If so next, time do this... lower your gearing as you approach the hill... once on the hill, pulled yourself forward on the saddle. This is will send more power to the pedals by using different muscles. Try to maintain a steady not choppy stroke. If this is difficult for you, practice a smooth stroke on the flats. Remember to relax up a hill not try and over power it. You overpower a hill when you know you can ride it.

Anyway, just remember to enjoy the ride.