Congrats on developing your first (Game Boy) game. The graphics are really nice. I love the jump animation and your colour palette. Your music really gave me a sense of urgency which fits the speed running theme.
It took me a while to get used to the controls due to the momentum of the player. The portal idea is nice although I didn't understand that I have to press A to enter them immediately. Sadly I wasn't able to finish your game because on leaving one portal in the second level (see screenshot) I always directly get throw into the spikes.