Many moms and moms-to-be spent more time on "worrying" ! It is because of the lack of knowledge on breastfeedng. Please go to attend some courses (you can check out www.lydialing.com or course organised by orgaisations like 母乳育嬰會) about breast feeding. After you get the knowledge, you get the confidence and no more worrying. It is the only key for success in breastfeeding if you are serious.
It has nothing to do with breast size. I had gestational diabetes, so I gained only about 8 kg during pregnancy, overall I was thinner than pre-pregnancy. However, I can still breastfeed my baby, he's 5 months now. The most important thing is that my baby sucks really well, and that helps to stimulate supply.
Blockage is not because of no milk. On the contrary, it's because you've milk inside and not being drained out properly, so it blocks your milk duct and the milk can't come out.
Good luck with your breastfeeding. If you ensure your baby can suck well (position is very important) and have faith in yourself, you'll succeed. Don't give up too easily.