Your instructors probably have given you some target speeds and power settings for a standard approach. The numbers are good guidelines for standard days... but as you're finding, we don't always fly on standard days (with standard loads, into standard airports). Frankly, I feel like a lot of flight instruction overemphasizes the formulaic and doesn't pay nearly enough time on developing a student's perception and ability to adjust.
The easiest time to make adjustments is when small errors have occured. A little high and fast on downwind is easy to correct. 15 knots fast and 50' high? No problem. Pull power back a little early. It's harder to bleed off 15 knots of airspeed and 50' of altitude when you're already 1/3 of the way down the runway...
If you're having a tough time with assessment, don't worry... that will come with time and practice. They say it takes a few hundred landings until a pilot is able to really accurately perceive high/low, fast/slow, etc.
I watched a nice video about engine out emergencies at cruise altitude / forced landings the other day. The instructor did a great job of asking the student about every 30 seconds to assess and adjust so they'd be sure they made their forced landing target. Can't seem to find it now, though.