I’m a beginner speed runner and this is the first game I’ve tried, while I know I should start with a normal no oob run I ended up trying oob first and I’m actually fairly consistent with every part of the glitch except for the second skew. I always end up undershooting it; I think it’s because I’m not holding the C stick long enough but I’m not sure. Are there any tips to help me get the timing better?

I'm going to assume you mean the skew into Biff's room rather than the 2nd skew, because Door Skip needs a skew but I don't think you're doing Door Skip. If you're not skewing enough to actually clip properly, then that means you're holding the C stick for too long. If you're skewing so much that you end up into the 2F hallway, then that means you're not holding it long enough. I'd suggest buffering it, but if you want to do it unbuffered then you'll have to just familiarise yourself with the timing through trial and error