The difference between the button combo for soft resetting and deleting your game is drastically different, as seen in the following:
Soft reset: press R + Start (L + Select works here as well) at the same time to soft reset
Delete saved file: press and hold Select + B + Up On the title screen to delete saved file
So as you see, you are in no danger if deleting your file, as you have to press a different combo on the title screen to delete, as opposed to soft resetting. Also note that if you DO by some miracle accidentally press the delete combo, the game will ask you about 3 times whether it is ok to delete the file.
Hope I helped!