Hi there, welcome to SimpleFOC!
Sounds like a very interesting project, please send us some pics 
I think you‘ve made your life a bit difficult by choosing the lowest spec components for all parts of the system:
- UNO is only 8bit MCU and very slow compared to modern 32bit MCUs
- L298N is not a BLDC driver. It is very old and slow transistor based tech. A modern BLDC driver uses FETs which switch much faster, and with far less losses
- AS5600 is only 12bits, and uses I2C (which is slow)
Personally, I would not switch to the Teensy, because while it is the fastest MCU we support, the support is not as good as with other MCU types. If you do go for Teensy, use a Teensy 4 and not a 3.
RP2040 like a RPi Pico would be an inexpensive MCU that works well, also ESP32 Wroom or S3 type MCUs are cheap and super-fast.
STM32G4 or STM32F4 MCUs are probably the best supported, and work very well, but cost a little more.
For the driver, please switch to a dedicated BLDC driver, any model you choose will be better than L298N. A SimpleFOC mini will work fine.
For the sensor, I would recommend a better sensor, with an SPI or ABZ type interface. AS5048A or AS5047P work well and are not too expensive.
I think once you improve your hardware you will find it easier to tune it. Getting it to stop precisely in angle mode will be a matter of having a decently fast main loop, and tuning the velocity and angle PIDs until you get a good result. You can also use the max-ramp (acceleration) and velocity limits, as well as the LPF (low pass filter) settings to tune the performance.
Please let us know how it goes