How do you visualize RNA on a gel?
You have two possibilities: When you only need a quick check if your RNA is ok and you indeed only get one band, you can try a "quick and dirty" method. Heat the sample for 5 minutes at 65°C and then immediately cool it down in an icebath and keep it there until loading. By doing so, you melt up the secondary structure of the RNA and keep it in this state. You will most likely then see only one band.

If this doesn't work or if you want to use a RNA size marker, there is no way around denaturating gel electrophoresis. Here you denature your sample in the loading buffer and then run a denaturating gel in which prevents the secondary structures. There is a good paper about this:


Denaturing RNA electrophoresis in TAE agarose gels


The classical method using formaldehyde (which is more dangerous in handling) is described in the following paper and also in the "Molecular Cloning: A Laboratory Manual" book by Maniatis and colleagues: 


RNA molecular weight determinations by gel electrophoresis under
denaturing conditions, a critical reexamination