Why are you using a tape measure, that's a builders tool for rough measurements mostly.
Furniture making techniques for your coffee table would be done with a rule and knife marks,
or not measured at all even, but four components planed to better tolerances instead.
You should be able feel within 1 thou of discrepancies. i.e...
The solution to this is having some hand planes for the job, and getting into a whole other realm of
refinement and precision which you couldn't get otherwise (without real expensive kit)
Have a look at the use of the shooting board, with someone skilled regarding the work,
like Rob Cosman for example.
He's as honest as you'll get regarding the work, (that's the important part)
but at the expense of interfiering sales pitches which some can't stand, that's his bag.
On the other end of the spectrum, there are a few prominent gurus on youtube who's income relies on keeping you as unskilled as is possible, but under the pretense of giving the answers,
or fooling you into thinking you already have the correct approach to things.
I won't mention who those guys are.
All the best anyway
Tom