U-boot doesnt execute a bare metal application properly

I recently compiled a u boot image from source, after I downloaded the source code from the official git repo i executed

make ARCH=arm CROSS_COMPILE=arm-none-eabi- distclean
make ARCH=arm CROSS_COMPILE=arm-none-eabi- am335x_evm_defconfig
make ARCH=arm CROSS_COMPILE=arm-none-eabi-

and then copied over the MLO, u-boot.bin and as some docs also mentioned it u-boot.img over to my SD card. After that i compiled this project: https://github.com/dwelch67/pocket_beagle_samples/tree/master/blinker01 (i verified that it works by dding the sdraw.bin to the sdcard and then letting it boot in raw mode from the SD card), copied the notmain.bin over to the SD card and wrote a uEnv.txt file with

boot_notmain=mmc rescan &&fatload mmc 0x40200800 notmain.bin && go 0x40200800
uenvcmd=run boot_notmain

to the SD card. After that i plugged the card into the SD slot of the beagle pocket and powered it on. However the LEDs didnt start to blink so either U-Boot or the notmain.bin file didnt get executed. If anyone has an idea what went wrong or could help me troubleshoot it please tell me.