Candace, Anthony is correct on your tranny thing. None are supposed to jump out of any gear.  I would certainly check all the bushings, The shift coupler at the transmission , shift rod guide bracket (holds one of the bushings) and the shift lockout plate. The guide plate and guide bracket are under the shift lever and are easy to service or repair. There is a "finky" adjustment on the lockout plate.that could cause you a problem with getting in reverse gear. Of course we are assuming your tranny is ok.
   Is your gear shift  lever"sloppy" or stiff to move, squeaks or rattles ?
   None of this "stuff" is really very hard to deal with nor is it very expensive unless the problem is with the tranny itself. But you have to know where the itch is before you can scratch it.
    Hey ! Did you say this was a 4 speed or a automatic ? If  its a automatic ,forget all of above.