Am I somehow stressing myself out?

I think you have identified something important here. It's not unusual to experience feelings that don't seem to match up with what your rational mind recognizes. 

In this case, it sounds like a part of you recognizes that the people around you do not find you "annoying and bothersome." Despite knowing that people like you, it seems that there's still a part of you that feels like you're a bother.

Finding a local counselor who can work with you to process those feelings might be just the help you need.

"Where you put your attention is where you will go". I forget who said this first, but it's very powerful. If all you think about and talk about is how annoying you think you might be, that will get annoying. Your intense self reflection is lovely; it will help you monitor yourself so that you're not affecting others negatively, but your alarm is going off too easily here and you risk having the opposite effect.

You don't have to be perfect. She's with you, so she probably likes you as you are. She seems to put far less emphasis on your possibly annoying traits. We all have faults and if that's what we focus on, that's all we will see. My hunch is that your most annoying trait might be your negative self-talk. How ironic is that?

There's another irony here...your goal is to be a better partner...but when you are self-critical, your focus is on you, not her. Every moment that fear grabs ahold of you is a moment that you're not being present in the actual relationship; you're gazing at your imagined faults. Fear steals your ability to focus on your loving partner. 

Maybe take a moment to image how she sees you...all of you. Put yourself in her shoes to see the entire you...how are you loving...thoughtful...a good partner? Confidence is a very attractive quality! 

I'm glad to hear you have friends and that your friends say they like you.

Trust your own sense of who you are which tells you that something feels uneasy within yourself.

Is the friend who says you're "just fine", very familiar with who you are?

"Friend" is a broad category.

She may not know you as fully as you know yourself.

Basically, it is possible to be "fine" and have some inner stress.

Follow your own thoughts and observations to more fully learn about yourself in ways your friend may not notice or be aware.