As programs get bigger, the time it takes to make progress goes up exponentially. Try to comment enough of your code and use well documented sub-routines. That helps cut down on debugging time as the program grows.
I think QBasic provides some memory space just for comments. If I remember correctly, you can comment up to about 1/4 of the total code but I wouldn't quote me on that. It has been quite a few years since I looked up if comments would unduely chew up memory in my programs.