The german � sound like lisp sound?

hello i have a question about the german � and my lisp and some other problems with letters i have been learning german for that last year and a half and i started looking up letter sounds and i checked every umlaut and played a recording of the sounds from the internet and my lisp sounds exactly like the german �. when i was young my uncle lived with me for awhile after him being in germany for a long time and over those years he had gained a german accent so he sounded german. The time he lived with us was from the time i was age 3 to age 8 and he was the main person around me my dad and mom both worked during the day and he watched me and picked me up from school is there a possibility that when i was young i got some of his german sounds mixed in and that giving me speech problems i got all the problems fixed accept the lisp how would i fix the lisp and would it be a true lisp or just a mess up with the � sound how do you make the normal s sound. i really want to fix this because im in 8th grade and to my opinion i think alot of the 8th graders are immature and whenever something comes up or they hear of the word lisp one of them will say something like whats a lisp? and then half the cl wil say a person that talks like travis and they try to imitate it yet they fail every single time and they think its funny like yesterday we were watching video on the presidents and we had to take notes and it said john adams had a lisp and like always someone asks and they start going with there immatureness please answer