No magic bullet that I know of
The only way that I know is to wait until it is set very hard then sand it smooth, preferably without going right through the existing coats, then re-coat with a very fine wide brush. If you sand before the finish is very hard you will get a nasty mess as the sanding pulls lumps out of the thicker sections of varnish.
If you can get a helper you could start from each end and finish in the middle. Then "dry brush" over the whole surface before it sets to ensure it is quite smooth all over. If no helper is available you have to keep a "wet edge" at all times and move very quickly. Since the temperatures are lower now you should have longer working time for the finish.
Now, if you had used shellac you could just refresh your rubber and work over the surface until it was perfect!
Hope this helps
David