I can only recall kanji when in the context of the specific sentence I learned it in. How do I fix this?
If you've been learning words using sentence cards or TSCs, and you have developed context-dependent memories of the words, that is not abnormal. It happens to many people. It goes away naturally over time as you continue reading with a dictionary and get more comfortable with kanji.
Beginners are more likely to form context-dependent memories. Word Cards may work better for them in particular, at the cost of slightly increased difficulty of reviews. But if you want to stick to TSCs and don't want to experiment with card templates, all you need to do to correct a context-dependent memory is look the target word up a couple of times when reading in the wild. Then your brain should draw the necessary connection, and it will stick.