Never saw a GFI with two load lines connected. Normally the other receptacles are wired in series. You'll never get good connection with 2 wires under the screw.
Correct way is to splice, (wire nut) the two wires to one coming from receptacle.
Every GFCI I have dealt with has two input terminals, and two output/load terminals. 4 holes per side (white/black) for a total of 8 holes for wires to be inserted in. They use a serrated plate inside that the screw pulls up against the wires. It actually works better with two wires as the plate and screw are square to the hole the screw passes thru.
Loosen the screw until it stops, don't force it, push the screw in as far as it goes, then insert the wires, stripped per the strip gauge, and straight, and put them in until they go no further, hold them in and tighten the living daylights out of the screw.
The line terminals in the pic posted by TLMGCAMP in
Post #7 are the ones that are burned. The ground is under them, indicating that the ground terminal is down and the line terminals are (on every GFCI I have ever messed with) is closest to the ground. The RV mfg used the GFCI as a junction to carry a portion of that circuit elsewhere, but not GFCI protected. My trailer is done the same way. Line in, and line right back out, plus the load out.
I got this pic from
this web page and they show the insides of some RV receptacles. Scroll down until you see Structure of Mobile Home Receptacles to see the pics.
Charles