Loosen up. Who says you have to be note for note? Note for note as the original artist did it is not that important - to me. Now note for note is important if you are playing melody, the tune, but, I do not play the tune I provide harmony. Do a Google on harmony; I think you will find that close is close enough in harmony. Now if you are part of the do it exactly school - no need to read any more of this post as it deals with building a bass line based upon the chords in this song, not playing by rote what the original artist did.
Our job, as I see it, is to call attention to the chord that is active in the song at this specific part of the song. The root note of that chord on the first beat - that chord is active does that, so at this stage in your journey concentrate on sounding the root note on the chord changes. Not before or after, dead on. Play from chord charts, fake chord sheet music. Need more in your bass line besides roots? The 5 works nicely. Need more? I like the 8, R-5-8-5 falls into a groove very well and most chords have a root, five and eight so the ole R-5-8-5 is generic and fits just about everywhere. Need more? Insert the correct 3 or 7 into your bass line. I go up to the 8 and leave the higher notes to the solo instruments. Root to eight keeps me busy.
Next thing to get into would be Walking to the next chord, I use chromatic notes because its easy. Look for the next chord's root; find it and miss it by three frets then walk to it and be on it for the chord change. Takes some timing, but, the walking notes are a piece of cake.
And yes go get with other musicians. Jamming in your garage with friends will advance your playing more than anything else I could point you to.
Should mention - and then comes rhythm. Melody, harmony and rhythm is what makes music. Concentrate on harmony now, rhythm next, and years from now get some melodic stuff into your bass lines.
Rhythm. For now be aware of the song's time signature. Most songs are in 4/4 time, (if nothing is shown you assume 4/4) however 4/4 is not used for everything. If the sheet music has 6/8 what beat would you use? Answer; 1-2-3-4-5-6 or any combination of 2's & 3's that add up to 6.... Yep rhythm and playing with other people will help your playing quite a lot.
If real live people are out of the question .... pull up a video of a song you like and play along to that. The playing along will tell you what else you need to be working on.