Writing, past tense and present HELP!?

Actually, the phrase "I have stumbled" (which you've contracted to "I've stumbled") isn't in the past tense. "I stumbled" is in the past tense, but "I have stumbled" is in what's called the "present perfect." You can look up that term for more information.

"I had stumbled" is in the "past perfect." In that paragraph, you're writing about actions that took place in the past (the huffing and the walking off) and also about actions that took place even further in the past (the tripping, the stumbling, and the stretching), things that were already in the past at the time that the narrator huffed and walked off. So what you need to do is combine the past tense with the past perfect tense like this: I huffed and walked off, dragging behind the bag that had tripped me.

I’d stumbled on it so many times in its year-long life that the rope you’re supposed to hold it by had stretched to at least two metres. The phrase "you're supposed to hold" is an example of what's called the "habitual present tense." It doesn't describe an action that is actually happening in the present ("I'm supposed to hold this rope"); rather, it describes an ongoing reality.

Anybody handling the bag, in the past, present, or future, is supposed to hold that rope.

In your case, yes. You walked off yesterday, but the rope's still stretched now. Past tense would also be correct.

You do need to decide what sort of impression you want your book to give. The first has a narrator who's specifically telling their story 'now'. If it was all past tense, it would just be a story in the past.

I prefer past tense.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.