Got to agree with all of the above. Great first attempt

You need to do the base to finish it off. Mix a little sand into some PVA glue (White glue) and paste it onto the top of the base and fill in the hole.
or
Fill in the hole with filler. Paint PVA glue all around the top of the base and then dip into some sand. Use your finger to clean around the side of the base before it drys.
When it is dry, paint it as required.