Well...embarrassed should be a skinny guy pushing bike up a little hill, or a 200+ couch potato watching TV all day long...
THERE IS NOTHING TO BE EMBARRASSED ABOUT WHEN YOU OVERWEIGHT AND ACTIVELY SPENDING YOUR TIME ON NOT SO EASY TASK /AT FIRST/ OF RIDING A BICYCLE TO IMPROVE YOU HEALTH AND QUALITY OF YOUR LIFE.
I'm 6.3 at 280+ at this moment. I look pretty good for my weight. I gain a lot when I quit smoking and then when I broke my back soon after that. Anyway, I always respected overweight riders more than "skinny butt" ones. Skinny butts doesn't have to work so hard... Don't be embarrassed...there is really no need for that.
If you don't feel comfortable in your area - just take your bike to some park and ride there. Its also a safer place to ride than on city streets or sidewalks, and you may meet pretty cool people there that share your cycling passion.
Keep riding guys!