It's possible you encountered either too advanced tracks (sounds like it) or missed a trick or two. After playing a lot of fullspeed tracks I can quickly spot some bad track design as well - though "bad" can also be interpreted in a way that there's some trick you need to know. If there's some unfamiliar thing causing failures I may watch and play against the world record times as some of the subtleties are hard to discover. These are easily found online.
Personally I don't like tracks with great deal of jumps & loops or no acceleration in the first half of the track. This is because if these conditions exist, the track actually becomes more difficult as those elements drain your momentum so much that the rest of the track becomes impossible if you make a slightest mistake in those early elements. Accelerator tiles are more forgiving usually, the tracks where you must drive through accelerator tiles perfectly to reach the finish exist but I see them less often on the servers I play as those jumps & loops tracks. Typically in "smooth tracks" if your wheels aren't oriented straight going in and coming out of loops and jumps, speed is lost or you crash at the edge. Line up to the loops/jumps early and avoid any drifting or wheels coming off the ground at any point of the track in these "smooth" tracks. Any corrections done inside loops really eat the momentum/speed.
Best beginner track in my opinion is Phase 2 by Socius. Most fun tracks are: ESL - Midnight Skillz` 3, Toxin Flash 2 and Wallride City. I can probably play them at my current skill quite easily even with a laggy computer and LCD, but it won't be nowhere as fun as on a low IO latency setup and for beginner with high latency LCD these are probably torture.
The learning approach I used for the more difficult fullspeed tracks was to download both the world record replay and another replay that's closer to the time that you can play. Watch the tricks in the world record replay and play against the one that you have hope of beating using the stuff in the wr replay.