A bit more information would help, including a sample of your code. If you will post one copy using the code tags {code=asm} {/code} (replace curly brackets with regular rackets) and another copy as a .txt attachment, that may help more.
If you are using the MPLab suite, then one possibility is that you are using tabs, but you don't have the replace tabs with spaces box marked (Edit>Properties>"asm" file types):
Oops sorry.In mplab I use tab sizes 4 or 6.When I going to place a code in this site I first copy the code to a notepad & do the alignment.After copy and paste it here.
[code]
mov a,b
hh (a few beginning spaces exist here and it's not lined up)
[/code]
This renders as:
Code:
mov a,b
hh
It will keep leading spaces. HOWEVER... in order to see it lined up as you type you would have to use courier. I set the font to courier between the code tags, but I should not have to.
In the original text, there are some leading spaces before the hh which were removed. The standard also likes to reduce multiple spaces to one space.
You can post large code fragments because you can scroll through them.
To actually see what I wrote in the edit box, quote my post. You don't have to post it.
More Options.. also provides Preview. I used a tag that won't render what's between the tags.