Your frame should be fine at this point but, if you go through water frequently, rustproofing the interior is a good idea.

Done right, you have to strip the frame completely with the possible exception of the headset cups. Use either Weigel's Framesaver (from most bike shops) or Amsoil HDMP (from most NAPA automotive dealers) and spray it into every tube including the chain and seat stays and fork blades Use the vent holes to get into the small tubes. Spray the coating lavishly into the tubes and rotate the frame frequently to distribute the liquid. Let it dry for a day or two and repeat. Do it outside and put plenty of newspaper under the frame to catch any drippings.