I'm on the side of "not wanting you to push too far too soon". Are you walking any kinds of distance right now? What is your current long distance per week that you are consistently doing?
I am also thinking that this race is doable for you, but not at a running pace. When you are still at 100 pounds to goal, you are carrying alot of extra weight with you. Trying to push a running pace for 13.1 miles in ten weeks, when you aren't currently running very much, is begging for injury.
There is certainly no shame in walking a half marathon. In fact, people are amazed at those kinds of distances when you tell them how far you really went. But saying that, you still need to train for the distance, even walking it is not an easy task.
Check with the race directors and see if you can switch up to the 5k distance if you still want to be able to run that day. Many events will allow a switch in distances.
Don't give up on your goal of running a half marathon. We just want to see you get there in a good state, and not get frustrated with injuries along the way.
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