Measure the inside of the flange from the lower opening edge up to the step (stop). The cement will act like a lubricant and allow you to push it down to that point. It will start to set in about 15-seconds after you push it on, so you only have that amount of time to mush it down. The cement acts by acutally disolving the plastic - softening it, and once the solvent dispurses, becomes solid again, welding the two pieces together. If you carefully measure so that you are sure the flange will go down as far as it needs to without sticking up, then it will work.
But, as noted, since you have a 4" drain, there are several types of flanges that can be used.
What you might want to do is take that piece you cut off (if you still have it), invest in an elbow or another coupling (pretty inexpensive) and make a practice connection just to see how it works. It is almost imposible to seat the coupling on the pipe dry all of the way to the stop, especially after priming (which removes both surface contaminants and makes it rougher) unless you have the cement on it to act as a lubricant.
You could spread some vasiline on it, slide it on to check the fit, then be very careful to clean all of that off before gluing it together - use a good solvent and/or soap to clean it up then the primer.
It is intimidating the first time you do it. Unless there is a defect in the fitting - like a knob of plastic sticking out - it will fit. My unprofessional experience.