Baby parakeets are tiny. How has it gone with this egg? Have you incubated it? Has it hatched?
The syringe I used to hand-feed Tiny (one of my baby 'keets) would jam and i often thought I should have ground up the hand-feeding formula even smaller than it already was, before mixing it with the warm water. The syringe-diameter was too Small for the formula-mix but still too Big for Tiny's little mouth.
I was terrified to injure the babies by hand-feeding them, and I only fed Tiny because she kept getting lost under the other babies, Mama wasn't finding her to feed her, so she would have starved without my assistance. (This meant, if I accidentally killed her, she was no worse-off than she would have been.) The same will be true for your egg If or When it hatches. (Since you don't have a Mama-bird to feed it.)
I don't know what the correct temp for a baby bird, but without a Mama-bird & nest-mates to keep the baby warm, it will need an incubator for warmth. Both before and also after hatching.
I looked youtube to get the idea of technique of How to hand-feed, but the one video that seemed most helpful, actually included instruction to do something (squeeze/massage the crop) that I THINK could've actually wound up killing a baby bird instead. I recommend Not to do this. Tiny got huge bubbles of air in her crop whenever I fed her, but it seemed to settle out after-a-while between feedings.
Without a mama-bird, a baby will need fed quite frequently, every few hours. Newly-hatched budgies are teeny teeny tiny!