The only thing I can really see is possible gear selection (though I don't know how you've got your transmission setup) when cornering. Aside from the F1 Long Tail I never use 1st gear at Sardegna aside from when I slightly miss a brake point and need to slow down even more.
Maybe it's just the way I setup my transmissions but I've found it's generally slower to run through first and shift into second than it is to just launch in 2nd. Not universal, but I generally find this true. Plus the rear tires won't step-out as easily on corner-exit in 2nd.
Also, I don't know how much downforce you're running but one can generally carry more speed through those two fast left-handers (the one at like ~45sec and the one at like ~1:10sec) but again, how the gearing is setup plays a big roll in corner speed as well. I just ran around there in the 962c and at these corners 2nd gear and 3rd gear, respectively, is what felt right. Only reason I mention it is I noticed you often take the first of these corners (the one at like 45sec... really wish I knew the names of corners at this track, lol) in first gear when the 962c can easily take it in 2nd, even with the stock gearing. Though if you're running long/wide gearing it may not be true for your setup.
Other than that I've no suggestions at all other than to just keep practicing throttle control. I was expecting you to be struggling around the track based on your description but you aren't slow by any means and certainly don't "stink"! There's time out there to be picked-up and you've got the skill to find it. Though if you're running mid-25min at Sardegna in the 962c I don't know how much time is actually left to find in that car. Maybe it's just me/my tune but the 962 is the slowest of all the Group 3 cars for me and a mid-25min time in that car seems pretty good to me. 787b can run it in 25min flat and quicker, so if you've got that car you should see how well you do in it.