There's no need to fret! That Jesus came from the line of Judah is very clear. Both the genealogy for Joseph (Mary's husband) and the genealogy for Mary are presented in the Bible, in Matthew 1 and in Luke 3 respectively, and both of these lead back to Judah.
The question most people ask, in fact, is how Jesus could also have been a descendant of Levi--the priestly order. This is where a little more ingenuity comes in with respect to tracing the lineage, and this is discovered via Elisabeth, who is said to be Mary's cousin (see Luke 1:36). She was "of the daughters of Aaron" we are told (see Luke 1:5). (We might infer, therefore, that Mary's mother or grandmother had been a descendant of the tribe of Levi.)
Here are snippets of the two genealogies, for Joseph, and for Mary:
1The book of the generation of Jesus Christ, the son of
David, the son of Abraham. 2Abraham begat Isaac; and Isaac
begat Jacob; and Jacob begat Judas and his brethren; 3And
Judas begat Phares and Zara of Thamar; and Phares begat Esrom; and
Esrom begat Aram; (Matthew 1:1-3, KJV)
23And Jesus himself began to be about thirty years of age,
being (as was supposed) the son of Joseph, which was the son of Heli,
... 31Which was the son of Melea, which was the son of
Menan, which was the son of Mattatha, which was the son of Nathan,
which was the son of David, 32Which was the son of Jesse,
which was the son of Obed, which was the son of Booz, which was the
son of Salmon, which was the son of Naasson, 33Which was
the son of Aminadab, which was the son of Aram, which was the son of
Esrom, which was the son of Phares, which was the son of Juda,...
(Luke 3:23-33, KJV)
NOTE: The spelling difference between "Judas" and "Juda" may simply be because in Greek a word has a different spelling when used as a subject as compared to when it is an object (or, as here, in the genitive case). These are the same "Judah" we see in the Old Testament.
In case we may still have had any doubts, Paul confirms Jesus' lineage.
For it is evident that our Lord sprang out of Juda; of which tribe
Moses spake nothing concerning priesthood. (Hebrews 7:14, KJV)
Jesus is very clearly a descendant of the tribe of Judah, as both his mother and Joseph had ancestry of that tribe.