We studied the accretion disc structure in the doubly imaged lensed quasar SDSS J1339+1310 using r-band light curves and UV-visible to near-IR spectra from the first 11 observational seasons after its discovery. The 2009−2019 light curves displayed pronounced microlensing variations on different timescales, and this microlensing signal permitted us to constrain the half-light radius of the 1930 Å continuum-emitting region. Assuming an accretion disc with an axis inclined at 60° to the line of sight, we obtained log(r_1/2/cm) = 15.4_−0.4^+0.93. We also estimated the central black hole mass from spectroscopic data. The width of the C IV, Mg II, and Hβ emission lines, and the continuum luminosity at 1350, 3000, and 5100 Å, led to log(M_BH/M_⊙) = 8.6 ± 0.4. Thus, hot gas responsible for the 1930 Å continuum emission is likely orbiting a 4.0 × 10⁸ M_⊙ black hole at an r_1/2 of only a few tens of Schwarzschild radii.