I Lied To My Mum Help Me!?

basically, i lied to my mum about goin 2 orchestra, wen i actauli just skip it and then go home and say i went. so now the concert is coming up and my mum asked abt it, and i said ill ask abt it. Then she found out from my newsletter that its TOMOROW!!!!!!!!! so wat do i do? i used 2 go 2 orchestra n i found it borin. i cnt jst appear in da concert wivout knowin any music n i really dnt want 2 tel my mum da truth cuz she'll absoloutly flip!!!!!!!!!! so im definetly not gna tel her da truth