I am cooking beef stew in the crockpot and accidentally put a little flour in the beginning not end
You should be fine, as long as you mix it in thoroughly.

Flouring the beef and browning is a very common first step, so there is maybe some in there already? Any extra flour to thicken needs some time to cook or it will make the gravy feel grainy.

Stir, stir, stir, and if you see any lumps, take them out. Be careful that this does not over-thicken the broth, as that might stick and burn during the simmering time that makes stew so stewy.