a bit of advice and reassurance please

long story short 2 of my closest friends from school have birthdays in june and july.
we were all doing our a levels so i couldnt really get the june person a gift coz of exams etc.

later in july now, i can get the july person a gift because it is now summer holidays etc.

i am kinda worried about the june person tho. i feel bad that i havent bought them a gift and i told my mum and she said not to worry and that i have left it a bit late but that isnt my fault coz of exams and they didnt have a party or anything etc. they came to my party and i paid for everyone including them and they also got me a gift.
June person is also very chill and accepting so i am sure they will understand. i went on holiday with june person and 3 others, i offered to buy something for them at the holiday but they didnt and it never really came up again.
it shouldnt be the case that material gifts buy a friendship but i got my other friends something and i just kinda feel bad ykkk.

my mum said that they have probably forgotten about it and to not worry. they didnt have a party and so they dont get a gift. they had a nice time with their family and thats it.

i am a little worried and i feel like i need to apologize. i 90% agree with my mum but yh :///

any suggestions??

much appreciated <3