I know it's hard, but the only advice I can give is slow desensitization, and learning not to care what you look like. I'm uglier'n'hell, in middle school my nickname was Zits'n'tits, on account of my horrible acne and man tits(no matter how much weight I ever lost never could get rid of these), but I just learned not to let what other people said or thought about me, hold me back, I started making fun of myself before others could and they didnt have any material to work with.
I worked at a restraunt where, we had a table, right in the effin' middle of the whole place, I was literally surrounded, any customer could see anything I did, and I'd think about what they were thinking about how I was making their food and them thinking about my long hair and it got ridiculous,I'd just take a few breathers or cigarette breaks in the back of the restraunt and push through it(my managers and the owner were aware of my agoraphobia).
Baby steps is the way to go, heh, If you've ever seen "What about Bob" with Bill Murray and Richard Dreyfuss in it. hehheh If you havent seen it, I'd recommend it, I dont think I've seen anyone with even just a scinch of Psychology/Phobia knowledge not laugh.
But, I dont know the landscape around you, make tiny goals, go sit on the bench for 10 minutes, who cares if you're not waiting for anyone or if it doesnt have anything pertinent to what you're doing.
My dad would have my agoraphobic uncle go into grocery stores, and of course all the "What if's?" come up, "Why're we going into a store with no intention of buying anything?" Well it's not illegal to enter a store and look around or sit down. It took him a bit, and wasn't easy, but his problem became more managable.
Best of luck to you.