Can't find a way to correctly print a string correctly with nasm

Question

I am writing a simple OS which prints all stdin (keyboard input) to stdout (the screen). I want to print a welcome string before the input. I'm using NASM since it is readable and easy to use.

I've tried two ways to print the string:

(Assume welcome is defined as db "Welcome to TextEditOS! Type whatever you want below.",0dh,0ah,0dh,0ah,0. Remove the 0 for #2.)

1. Using a loop similar to a while loop. Originally I used bx instead of si since a few tutorials did it that way, but this answer suggested using si since bx is used for the page number and color in TTY mode.

mov si, welcome
mov ah, 0eh

printWelcome:
    cmp [si], byte 0
    je mainLoop
    mov al, [si]
    int 0x10
    inc si
    jmp printWelcome

2. Using int 10h where ah=13h. The code I used is something like this, though I believe I have the original code on my home computer (I'm away right now, will update this question once I get back).

    xor ax, ax
    mov es, ax
    xor bh, bh
    mov bp, welcome

    mov ah, 0x13
    mov bl, 0ah ;this was something else I think
    mov al, 1   ;write mode
    mov cx, 56  ;length
    mov dh, 0   ;x
    mov dl, 0   ;y

    int 0x10

Both of these work just fine in QEMU. However, when I burn the full code onto a USB flash drive and boot it, the first way prints around 1-2 screens of invisible characters before stopping in the middle of the screen, and the other seems to print an @ and nothing else. The rest of my code, which is the keyboard input, works fine both ways.

Here is the full code for my operating system:

[org 0x7c00]

jmp short start

db 90h,90h,"TEXTOS",20h,20h

section .text

start:

; First, let's set up the stack
mov bp, 7c00h
mov sp, bp

; Insert either way I used to print the string below

; end print func

mainLoop:
    mov ah, 0    ; get keyboard input
    int 16h
    mov ah, 0eh  ; print char
    int 10h      ; al already has the char to print
    cmp al, 13   ; is char 0dh?
    je newLine
    cmp al, 8    ; is char 08h?
    je backSpace
    jmp mainLoop ; loop

newLine:
    mov al, 10   ; complete \n with 0ah
    int 10h
    jmp mainLoop

backSpace:
    mov al, 32   ; insert space over last char
    int 10h
    mov al, 8    ; then another backspace to go back
    int 10h
    jmp mainLoop

welcome: ; welcome message
    db "Welcome to TextEditOS! Type whatever you want below.", 0dh, 0ah, 0dh, 0ah, 0

times 510-($-$$) db 0
; Boot signature
dw 0xaa55

Commands used to compile and run:

nasm boot.asm -fbin -oboot.img
qemu-system-x86_64 -drive file=boot.img,format=raw

As said above, I will find the code for #2 and edit this question with it. I will also try to upload some GIFs of what I get on real hardware.