When the frequency is set out of the ham bands, depressing the PTT button ought to give you an ERROR display. The radio is designed to prevent out of band transmission.
Check your manual for other ways to save frequencies. Don't have the manual? There is one at this URL: http://www.dis.org/radio/radios/ft50/ft50_manual.pdf
I had a quick look at that manual & learned that saving memory involves several steps with the F/W button. Too involved to condense for you here. The procedure is on page 27.
From what you wrote, you did not quite do the right things to expand receiver coverage. First set the radio to operate in VFO A or B. Momentarily pressing the knob recalls the preset band-ranges for tuning and scanning. To reset for expanded range, hold the knob and LAMP button depressed while turning the transceiver on.
Note that you need to enter the AM mode for receiving aircraft communications. That procedure is on page 25.