What if I feel uncomfortable about sending it?

Many writers and artists are very nervous about facing the rejection and criticism of their work; it's the equivalent of a singer performing in front of a large audience. If you don't feel it's ready, set it aside for a month or two and don't look at it; when you pull it back out and review, you'll have a bit of distance from it and mistakes stand out much better. If you feel that it represents your best efforts, step outside of your comfort zone and submit it. Know that regardless of how good your work is, there are always going to be people who don't like it; however, your critics will be the most vocal about your weak points, guiding you toward areas you can improve. In short, though, you undoubtedly created your comic because it's a passion, and the only person whose opinion about it that matters is yours.