Plannar Inductor Unacounted Parasitic Capacitance
Using equation 2 from page 3 of this white paper on distributed capacitance
It covers the 300pF you describe.
\$Cd=\LARGE\frac{(\frac{1}{2\pi(SFR)})^2}{L}\$
When \$SFR = 2.899MHz\$ Then \$Cd=1.005nF\$
At the predicted SFR, that is your 1nF parallel cap
When \$SFR = 2.534MHz\$ Then \$Cd=1.315nF\$
At the actual SFR freq there is an additional 300pF!