mag floats are great for cleaning the glass but they do nothing for uneaten food. and those little bowfront tanks are usually plastic, not glass, so the mag float would probably scratch the heck out of it.
feed less, and use a piece of airline tubing to suck out any uneaten food a couple hours after feeding.
on a side note, your betta would be much happier in a larger tank. a 2.5, a 5 gallon, or ideally a 10 would be great! and with a 10 you have the option of having a few tankmates, depending on the betta's personality (if he will 'play nice', lol).