If you're just learning, go nuts, plan to upgrade in a year or two, I bought a xr100r for my wife, its perfect for her but there are so many more comforts to a slightly larger bike (including not feeling the rough gravel roads through the narrow front tire). you can use that xr100 to get really comfortable with the sport in general and then upgrade once you have mastered that little thing... you know whats fun, not being afraid of your bike.
the wieght is probably not an issue for one or two seasons and regardless of your weight you'll want to upgrade in a couple years for oa number of other reasons, we all want another bike eventually.
having said that Im 260lbs and i have put the little xr100r through a couple casual trail rides with the nephews and its held up to my weight just fine, torque wise it had all the power got through the muddy spots and over a few big tree branches, no jumps! all i could ask for out of a bike i was too heavy for. when i didnt have my own klr250 with me.
for what you bought, enjoy the crap out of that thing and plan to upgrade in a year , two tops.